The Thestral-drawn carriages returned to Hogwarts castle in the first week of January, bringing with them the students who hadn't decided to stay at school over the Christmas holidays. The spring term had begun, and it was so far keeping Artemis even busier than the first.

The Quidditch season was in full swing, and Murphy McNully had the Hufflepuff team practising twice weekly in preparation for their second match of the year. They would be up against Gryffindor, who would, according to Murphy, be their "most challenging opponent, statistically speaking". Artemis was training harder than anyone; their best chance of winning involved her catching the Golden Snitch before Charlie Weasley, and she knew for a fact that Charlie had never failed to catch the Snitch in a house game before, nor in any of the friendly games she had played with him. Still, there was a first time for everything, and she was determined that this would be it.

As for lessons, the workload had increased in all five of her subjects, with each of her teachers stressing how many - or rather, how few - months remained until the start of the N.E.W.T. exams. And the N.E.W.T.s were not the only exams that Artemis would be preparing for; having missed the Apparition classes her friends had taken the year before, she had re-enrolled on the course in the hope that she would be able to take her exam at Easter with the current sixth years.

She had assumed that she would be the only final year student taking the classes, but when she arrived in the Great Hall for the first one, she saw that Corey Hayden was also there, having spent half of the previous year as statue. It was lucky that they were friends now, Artemis thought, as Corey waved to her from across the hall and she went over to join him.

"Now that we are all here," said the wizard at the front of the hall, whose wispy pale hair was instantly familiar to Artemis, though she wasn't sure where from, exactly. "Welcome to your first Apparition lesson. My name is Wilkie Twycross, and I will be your instructor for the next twelve weeks."

"Oh!" Artemis said out loud, now realising whe she had seen the wizard before. Corey gave her a quizzical look, and she whispered to him, "I met him in the Magical Transport office when I was there for the morning in the summer."

"You mean the morning the Japanese Ambassador's Portkey was stolen?" Corey asked, and Artemis nodded. "Do you reckon he had something to do with it?"

"No, it was a wizard in disguise. Burke. He's a Metamorphmagus, remember?"

"I know, but he probably wasn't working alone. From my extensive reading of crime novels, I've realised that criminals often work with accomplices. And usually, things are quite as they seem. Often, it's the person you'd least expect that is the one who is actually behind the crime," he lowered his voice as Professor McGonagall frowned at him. "For example, in one of the Conebush and Persimmons stories-"

"Shush, Mr Hayden," said Professor McGonagall, and Corey fell immediately silent. Artemis waited for McGonagall to look the other way before whispering back:

"I really don't think it was him. I mean, I just can't see him being a criminal mastermind."

"And don't forget the three Ds of Apparition!" Twycross was saying. "Destination, Determination, and Deliberation!"

Artemis raised her eyebrows at Corey, who frowned.

"Yes, okay. You have a point," he whispered to her.

Professor McGonagall gave them both another firm stare, and so they stopped talking for the remainder of Wilkie Twycross' lecture. Once he was done, Twycross set all the students about practising how to Apparate into hoops a few feet away from them, though not many students were having much luck so far. Even Artemis, who had experience with side-along Apparition thanks to Jane Court, Bill Weasley, and Kingsley Shacklebolt all having Apparated with her, had to admit that it was a much harder feat when doing it without someone else's help.

"Remember, fix your mind on your destination," Wilkie Twycross called out, his voice monotone. "Then make sure that you are determined to be present at said destination. Then, when you turn, move with deliberation."

Artemis rolled her eyes. So far, she had been staring at her hoop with what she thought constituted both determination and deliberation, but had yet to enter it despite four attempts at doing so. Did Twycross not have any more useful advice than reciting words beginning with the letter D?

"Miss Hexley," Professor McGonagall said as she walked past. "Perhaps I might remind you that Apparition is a form of self-Transfiguration?"

She pursed her lips into a tight smile, and after a moment's consideration, Artemis grinned. She had always been good at Transfiguration, after all. And McGonagall had a point; if she thought about it, Apparition was just Vanishing and Conjuring. She could do both of those things. So, for her fifth attempt, she stopped staring at her hoop, and instead closed her eyes, envisioning herself disappearing and reappearing inside it, and immediately turned around on the spot.

BANG!

A sound like a firecracker echoed in Artemis' ears. She opened her eyes and looked down at her feet, and found that she was standing in a hoop. Delighted, she looked up to meet Professor McGonagall's eye, but as she did, realised that she was standing not a few feet, but several metres away from where she had started, and was currently occupying the hoop of a sixth year Ravenclaw girl.

"Sorry," she muttered, stepping out of the girl's hoop and walking back across the Great Hall to her own, Wilkie Twycross already droning about the first D as she did so.

"How did you do that?" said Corey, swaying slightly from all his so far fruitless turning on the spot.

"The fourth D," Professor McGonagall said quietly, giving Artemis an almost imperceptible wink. "Deviation."

***

Between Apparition lessons, N.E.W.T. revision, and Quidditch practice, Artemis was busier and more tired than she had ever been before, however, there was at least something fun to look forward to. The first Hogshead weekend was approaching, and having finished his most recent placement with Gringotts Bank and having a few weeks off for study leave, Bill Weasley had arranged to meet Artemis in town.

In Jacob's absence, Bill had always been like a big brother to Artemis, and with him having been out of the country since the beginning of the summer, she was excited to catch up with him. After all, a lot had happened since they had last seen each other in person.

"Wow," said Bill as Artemis finished recounting the events of the previous six months, his blue eyes wide. "You weren't joking."

Artemis shook her head. "I never joke, Bill. I'm always very serious."

"Okay, but let me get this straight," he replied, blinking hard. "One of the members of R is a Metamorphmagus and stole an international Portkey in order to transport an escaped convict from Japan into the country."

"Shiratori, yeah."

"And since then, Shiratori has been leaving messages for R in Japanese, disguised as white quills. And you saw someone in a cloak take one of the messages from the Whomping Willow on New Year's Eve."

"That's about it," Artemis nodded. "They had Sickleworth with them. He snuck under the tree and got it for them. We found another white quill on him before, as well."

"Right," Bill frowned. "Where is Sickleworth now?"

"My uncle came back from South America at the start of the year. I've given Sickleworth to him to look after. Hopefully he will cause less trouble in Dorset."

"He might. Gringotts will probably want him back eventually, though. Or not. That Niffler is a menace. I swear the poor bloke who lost him was actually relieved to finally be rid of him."

"How do you lose a Niffler, anyway?"

"You're asking me. Sickleworth's keeper was called to visit the Head of the Department of Magical Artefacts back in the summer, and the Niffler did a runner. Ran down all the way to the Department of Mysteries, and no one was able to catch him."

"I remember that, actually. Charlie told me he was trying to steal crystal balls."

"Well, they are shiny."

Artemis nodded, and though she laughed at Bill's comment, her mind began to wander back to the black door she had seen on the second lowest level of the Ministry of Magic.

"Bill," she said, frowning deeply, "do you know what they do in the Department of Mysteries, exactly?"

"No, no one does. It's why they call them Unspeakables."

"That's what Olivia Green said. Jacob's old friend, she was at the trial," Artemis explained, seeing the quizzical look on Bill's face. "She works in the Department of Mysteries now. Something to do with prophecies. Maybe she's in charge of the crystal balls!"

"Maybe. All I know is that no one really applies to work in the Department of Mysteries. They send out letters to the people they most want to join them the night before they get their N.E.W.T. results," Bill told her. "It's always the people with the highest grades the next day."

"Did they write a letter to you?"

"Yes. I considered it, actually."

"You did?" Artemis' eyes widened. "But you've always wanted to be a Curse-Breaker! You had a job already lined up at Gringotts."

"A job Rakepick helped me get. The letter came through just after she betrayed us in the Buried Vault, so I thought maybe I'd be better off without it. But then I decided that I wasn't going to let her stop me achieving what I'd always wanted, so Gringotts it was."

Bill gave Artemis a wry smile, which Artemis didn't return. As the two of them walked past the Shrieking Shack, they stepped off the curb to allow a grey haired witch in a St Mungos uniform to pass them on the pavement. Once she passed, they stepped back up again.

"Talking of Gringotts," continued Bill, "you know the application deadline for the Curse-Breakers' training scheme is the end of this month, don't you? Have you sent off your application for, yet?" Artemis shook her head, and Bill sighed. "Why not? What are you waiting for?"

"A professional reference." Artemis pulled her rucksack off her back and held her form out to Bill. "I thought you might like to write one for me."

"Really? I'm not sure-"

"You don't have to if you don't want to."

"That's not it," laughed Bill. "I just don't know if I'm the best person to write you a professional reference."

"Why not? We've broken curses together, we were apprentice Curse-Breakers together, you work for Gringotts now..."

"In a very junior role!"

"Yeah, well. It's not like I can ask Rakepick, is it?" Artemis muttered darkly.

"I guess not. Go on, then."

Smiling, Artemis handed Bill her application form. "I've filled out everything else. You just need to do the last page and then I can send it off."

"I can hand it in for you later."

"Yeah, that would be great. Thank you." Artemis wrapped her arms around Bill's waist. "I've really missed you, you know."

"I've missed you too, little one." Bill ruffled Artemis' hair, and for once, she didn't stop him. They broke out of their hug and he frowned at her as he asked, "Are you worried about all this R stuff?"

"Sort of."

"What about the others? Penny and Tonks and Charlie?"

"Um..."

"You have told them all about this, haven't you?"

"Not really," Artemis bit her bottom lip. "I mean, Tonks knows a bit because she was doing work experience with the Aurors, and Charlie knows about Sickleworth because all the prefects had to help find the thief. It's just that Penny said that the Cursed Vaults are all finished with now, so we should try to forget about R and all that."

"Not if they've been passing messages to someone on the school grounds you shouldn't," Bill shook his head. "Have you been able to talk to anyone else about it?"

"Yeah. Kingsley Shacklebolt is in charge of the investigation, and I said about it to Corey Hayden who got turned into a statue. He was there with me when we saw the person getting the messages from the Whomping Willow on New Year's Eve."

"So, whoever has been sending these messages was at school during the Christmas holidays," Bill nodded. "Okay, that narrows things down. Who was there?"

"Me, all of the Circle of Khanna except for Barnaby, Corey Hayden - but he was with me when we saw the messenger - and then some of the teachers. Snape, McGonagall, Dumbledore, Flitwick, Sprout, Hagrid. That's it," Artemis frowned. "But none of them would be working with R. We know we can trust all of them."

"Can we?"

"Yes. It wouldn't have been any of them. Anyone might have walked into the grounds that night-"

"You said that they were walking from the castle."

"Or Apparated!"

"You can't Apparate on Hogwarts grounds."

"I did it just the other day."

"They lower the enchantments for the Apparition classes," Bill said, his face grim. "Artemis, I know these people are all people we know, but think about it. We all thought we could trust Rakepick, Jacob thought he could trust R..."

But Artemis shook her head, stubbornly refusing to consider what Bill was telling her.

"No. These are our friends. There must be an explanation, someone must've come in by a secret passage or..."

As she spoke, Artemis noticed two flashes of red hair outside Zonko's joke shop. The Weasley twins must have snuck out of the castle again. She had an idea.

"Never mind," she said to Bill. "I just know it wasn't anyone in the Circle of Khanna. No one would betray Rowan like that."

"But-"

"Don't you think it's a weird place to leave messages for someone, right under the Whomping Willow? It seems like you're asking to get Whomped."

"Are you changing the subject, Hexley?"

"I might be, Bill. I might be."

***

Bill may have given up on trying to persuade Artemis that she may not be able to trust one of her friends, but she had not given up on the idea that someone else may have entered the grounds that night via one of the castle's many secret passages. At dinner that night, she made a note of where the Weasley twins were sitting, and as soon as she saw them leave the Great Hall (their pockets looking suspiciously stuffed full), she followed them out towards the grand staircase.

"Fred! George!" she called after them, and they both struck overly nonchalant poses.

"Hey, Artemis, what's up?" asked Fred, his voice consciously casual. Artemis rolled her eyes.

"I don't care what you two are up to with the Zonko's products you bought earlier," she told him.

"How did you-"

"Never mind that. Do you two still have the map you found in Filch's office last year?"

"Yeah, why?"

"I need to know more about the passages in and out of the school," Artemis told them. "Didn't you say there were a few even Filch doesn't know about?"

"There were four," muttered George, with a dark look. "But after your brother used the one in the lake house last year, we're down to three."

"And one of those we can't even use," Fred sighed deeply.

"Why not?"

"Because it goes from right under the Whomping Willow."

Artemis' eyes widened. "What?"

"The passage goes from under the Whomping Willow," George repeated his brother's words. "Really, Artemis. Do try and keep up."

"Where does the passage go?" Artemis asked, ignoring the twins' dramatic eye rolls.

"We don't know. It disappears right off the edge of the map."

"So, you've never tried to find out where it goes?"

"Of course we haven't!"

"You have seen the Whomping Willow, haven't you? No way we'd go down there."

George shook his head. "We can be reckless-"

"And over-ambitious," Fred chipped in.

"-but we are not..."

"We are most definitely not..."

"Stupid." The twins finished their sentences in perfect unison.

"Well, you could've fooled me," Artemis sighed. "You don't happen to know of anyone who might know where it goes, do you?"

"No," George shrugged his shoulders, looking a little like Charlie as he did so. "Sounds like a pretty good way to get killed, if you ask me."

"So maybe you should try asking the ghosts," said Fred. "We've got stuff to do right now, anyway."

Already tired of the twins, Artemis sighed heavily and left them to whatever it was they were doing with their bag of Zonko's products, which smelled suspiciously like dungbombs.

***

The following weekend, the third Quidditch match of the year was taking place, with Ravenclaw playing Slytherin. Having taken on the Slytherin team earlier in the year and experienced their new Captain's strategies, Artemis couldn't say that she envied the Ravenclaws, nor fancied their chances. It didn't appear that Andre Egwu, the Ravenclaw Keeper and now Captain, did either; Artemis had never seen him look so nervous as he did at breakfast on Saturday morning, though his robes were as pristine as always.

Artemis made her way down to the Quidditch stands with Penny and Tonks - Chiara already stationed on the pitch, having volunteered to help Madam Pomfrey provide first aid if required - ready for the start of the match, but as the girls walked through the grounds, she noticed someone walking in the opposite direction, away from the Quidditch pitch and towards the Whomping Willow. As they had been on New Year's Eve, the person wore a hooded cloak, which completely obscured their face.

"I won't be a minute. Save me a seat," Artemis told Penny and Tonks, before disappearing under the stands to transform into her Animagus form and, cat-shaped, running across the grounds in pursuit of the hooded stranger.

From a slight distance, she watched as they paused near the Whomping Willow, just out of reach of its moving branches. That was exactly what they had done on New Year's Eve, Artemis thought, but that time they had sent Sickleworth in to dive beneath the tree. Now that Sickleworth was in Dorset, what would they do? Surely, no one would so stupid as to try to climb underneath the Whomping Willow themselves...

Luckily for them, the person in the hood had some sense, though Artemis herself could not make any sense of what they were doing. They removed their wand from their robes and used it to levitate a stick, which under their guidance floated towards the tree and poked it gently near the base of its thick trunk. Instinctively, Artemis moved backwards, but instead of lashing out, the tree stopped moving entirely. The cloaked stranger lowered their wand, walked straight up to the tree, and disappeared beneath it, the Whomping Willow not even stirring as they did.

Artemis looked over her shoulder before switching back into her usual girl-shaped form, and frowning, went over to investigate. She had never dared go so close to the Whomping Willow before, having always wanted to keep as many of her bones unbroken as possible, but now that it was motionless, she was able to walk straight up to it. Now that she was in close proximity to the tree, she could clearly see that its twisted roots looped around a hole beneath the base of the tree.

"Lumos!"

The tip of Artemis' wand lit up, and she shone it down the hole. There seemed to be a tunnel in the ground beneath, though it was too dark to get even an inkling of where the passage might lead to, even with Artemis' bright wandlight and winter sun illuminating its entrance.

A shadow appeared over the roots of the tree, and there was suddenly less light entering the tunnel. Something was blocking out the sunlight, and whatever it was, it was moving. Artemis' heart skipped a beat, and she stopped looking down the hole, instead turning her face straight upwards. Above her head, the Whomping Willow was beginning to stir.

Quick as a flash, Artemis leapt away from the tree, and not a moment too soon, because a split second later, a clubbed branch slammed down to the ground at the exact point where she had just been standing. A second branch descended on her, and she jumped out of its way and began to run as fast as her feet could carry her, dodging every blow the Whomping Willow aimed at her. She was almost out of its reach when a whip-thin tendril-like branch caught her leg, and started to wrap around her shin.

"Diffindo!" she shouted, pointing her wand at the thin tree branch.

It broke, but her relief was short lasted. Another branch, much thicker and more forceful than the last, was heading straight for her. She flung herself out of its reach, landing heavily on the ground. Above her, one more branch flew down through the air, and she only just managed to roll out of its path. It struck the ground with a loud thud that reverberated through Artemis' body, but did not hit her.

She scrambled to her feet and moved even further away from the tree, which seemed to calm down, as if it knew that she were now safely out of its reach. Her heart still pounding in her chest, she looked down at herself. She was filthy, covered in dirt and grass stains, she had a cut on her shin, a hole in the knee of her jeans, and grazes on her arms, but otherwise, she was unharmed.

Fred and George were right, she thought to herself as she limped back up the path away from the Whomping Willow, trying to get into that passage wasn't just reckless, it was stupid. And yet, the stranger in the cloak had managed to make the tree freeze, and had descended below it without getting so much as scratched, let alone whomped. So clearly, it was doable if you knew how. But who would know how?

The answer came to Artemis almost immediately. Jacob. Her brother had uncovered almost all of the secrets of Hogwarts castle during his time at school. But, seeing as he was now in Azkaban prison, she would have to find the next best thing. She smirked to herself. Yet another thing Fred and George had been right about; she really was better off asking one of the ghosts.

***

Duncan Ashe, Jacob's former best friend and erstwhile lover, now haunted the prefects' bathroom on the fifth floor of the castle. He and Artemis were not on the best terms, and she would usually have brought Charlie along with her to mediate, but given that he would still be watching the Quidditch, she was just going to have to deal with Duncan by herself.

As Artemis predicted, Duncan was not all too happy to see her.

"What do you want this time?" he asked, glaring at her over the top of a toilet cubicle.

"I need to ask you something."

"Go on, then," Duncan sighed heavily. "Get it over with so I can get back to my haunting."

"It's about the secret passages around Hogwarts," said Artemis. "I need to know where one goes to, and I thought you might know."

"Why can't you just go and find out for yourself?"

"I tried that, but the passage is guarded by the Whomping Willow."

Duncan's features froze, and his ethereal body seemed to stiffen.

"What do you want to know about the Whomping Willow passage for?" he asked, his voice almost hoarse sounding.

"I've been seeing someone coming and going there, leaving and carrying quill messages. I thought they might have something to do with-"

"The Cabal."

"Yeah," Artemis nodded. She tilted her head to one side, trying to read the expression in Duncan's eyes. "You know exactly where that passage goes to, don't you?"

"It goes to somewhere R liked to use as a meeting place back when they first made contact with your brother. It was close to the school, so close that they could keep watch on us, and it had a passage that went straight here."

"Yes, but where exactly is it?"

"The Shrieking Shack," said Duncan. "It's a clever place to choose. After all, no one would have found them unless they knew they were there."

"But the Shrieking Shack is right in the middle of Hogsmeade!" Artemis wrinkled her nose. "Wouldn't someone notice something?"

"Not necessarily, no one ever wants to go there, not even the ghosts. That's the beauty of it, I guess. It's hidden in plain sight," Duncan frowned, and cast a glance at the mermaid gently snoring in the stained glass window before turning back to Artemis. "You say that there have been quill messages and someone has been going in and out of there?" he asked, and Artemis nodded in response. "That's not good. It means that they're planning something."

"It does?"

"Yeah. That's how it started. After your brother discovered them, that's how we first started making contact. We'd go there to meet one of their members."

"Who?"

"I don't know, we always called her 'The Director'. I got the feeling that she was their leader, or maybe second in command. Anyway, Olivia hadn't been keen on us meeting with R from the start, and she really didn't like the Director, so she left us. The two of us kept going, but then... Well, there was someone else sending messages, too. Not long after that, I died."

"Duncan," Artemis frowned. "How did you die, exactly?"

"We were instructed to prepare to fight the dragon in the Buried Vault, and Jacob suggested using a potion, as dragons have spellproof hides. We made one together from a recipe Jacob found, and I noticed that he was adding Erumpet horn instead of Bicorn horn. The cauldron was going to explode, and he was right next to it, so I pushed him out of the way," Duncan shivered, and Artemis noticed for the first time that the ends of his hair were singed. "I saved Jacob, but I couldn't get out of the way quickly enough."

"You said before that Jacob killed you."

"The potion was his idea, he came up with the recipe, he added the Erumpet horn. He even found me and apologised for killing me."

"Because he felt like it was his fault, not because he actually killed you!" Artemis glared at Duncan. "It was an accident all along!"

"But don't you see? He found the recipe, but he never said where he found it. And Erumpet horn wasn't on the ingredients list. Jacob was good at potions, he'd have known not to put it in, and he'd have known the difference between that and Bicorn horn," Duncan shook his head. "He came to apologise, he said he wished that things had been different, but that it was the only way. The Cabal said they needed a sacrifice in order to get what they wanted."

"What did the Cabal want?"

"He didn't say exactly, but I'm guessing they wanted whatever was in the final Vault, because he told me that he had found a way to break all the Curses and end the Vaults once and for all, he just needed to buy himself time to do it. Because until he'd achieved that they wouldn't stop coming."

"Coming for what?"

"Him. You. The school, and everyone in it," Duncan's expression was grim. "Whatever is in that final Vault must be powerful beyond imagination, because these people, the Cabal, they will destroy everything that is in their path in order to get it. They will lie and betray and hurt and kill, because they don't care about anything but the Vaults and the secrets they hide. I don't think there is anything that they would not do. They'll stop at nothing, and they won't stop."

"Unless someone stops them," said Artemis.

"No one can stop them. Even Jacob knew that. There's only one way, and that is to break the Curses before they do," Duncan replied.

"But what if-"

"There is no what if. They will not rest until the curses are broken, and while the Cabal and the Cursed Vaults are still out there, none of us can rest either. None of us is safe, and none of us will be truly free."

Duncan let out a deep and mournful sigh and floated away, disappearing through the far wall of the bathroom, leaving Artemis with only the sleeping mermaid in the stained glass window for company.