Apparition lessons began in October. Their teacher, Professor Miller, from the Ministry of Magic, kept telling them about the three D's—Determination, Destination, Deliberation.

If they followed these, they were supposed to move from their place, where they were standing in a vacated Great Hall.

There was no progress whatsoever in the first three days, but Remus finally managed it on the fourth day, among the cheering of the Gryffindors and dark looks of the Slytherins.

To nobody's surprise, James and Sirius managed it too, at the end of the day, together. James landed just in front of Snape, making the latter stumble and fall backwards in shock. Sirius appeared beside Avery, who did not fall however, so Sirius was apparently so stunned at his success that he whooped and knocked over Avery.

"Please stop playing the fool, Potter, Black," said Professor McGonagall loudly, above the laughter of the rest. Lily pursed her lips in disapproval, but didn't say anything.

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Few days later, the Daily Prophet showed that the Dementors of Azkaban had left the wizarding prison and were, as such, roaming around wherever they wanted.

The older students look a grim view of this, as did the teachers.

"It's a bad sign that the Dementors are supporting Voldemort," said James, when the Marauders were discussing that in the morning.

"Yeah. I think we should learn to defend ourselves against them," said Remus.

"The Patronus charm, you mean?" asked James.

"We don't need it, Remus! Dementors feed on sadness and despair," said Sirius, grinning. "We sadly lack that."

"This is not a matter to joke about, Sirius," said Remus sternly. "We'll join the Order after a few months—we need that defense."

"All right, then. But where do you suppose we get a Dementor to practice on?"

Remus silently contemplated on it.

"Let's ask Professor Barten," he said at last. Professor Barten was their new Defense teacher, who was both friendly and also knew the subject very well.

Professional Barten approved of their decision.

"It's not an easy charm. I won't teach it in class; no one will be able to produce a Patronus. Pettigrew, if you don't mind, I think you haven't quite got the right temperament for this spell."

Peter went red.

"Try him, Professor," said James.

Barten grinned. "Right, I'll try all of you." He gave them a time in mid-October.

As they trooped in the classroom that day in the evening, they saw for the first time what a Dementor looked like.

"It's just an impression I created, not real, Pettigrew," he said when Peter whimpered.

Real or not, its behavior and power seemed real. They felt cold and clammy. Suddenly they were reliving their worst memories.

James and Peter walked back to the back of the classroom as Barten directed.

Sirius and Remus couldn't.

Sirius felt unsteady on his feet. He kept remembering his worst moments with his family—the moment he had found out that Regulus had joined up, the moment his family disowned him, the moment their father had cut off the head of their family's house elf before Kreacher. Then he remembered the time James and Remus were cold-shouldering him, the time he had felt he had lost his only family, and James having the Cruciatus curse cast on him by Voldemort.

Remus was white as a sheet. Every transformation of his before his friends became Animagus began to play in his mind clearly; it felt as if they were happening all over again.

"PADFOOT! MOONY!"

James and Peter dragged their friends to the back of the classroom, where Professor Barten's goat Patronus, a shining silvery-white thing, was circling.

Sirius and Remus came back to earth again.

"Not to worry," said Barten assuringly. "You'll soon learn learn to repel it."

He taught them the spell—Expecto Patronum—and told them that they needed to concentrate on their happiest memory to produce a Patronus.

"James, you go first?" he said.

James did. As the memories of the Cruciatus curse, his grandfather's death and Lily shouting at him that she hated him began to surface in his mind, he strongly concentrated on his first Hogwarts' train journey—the day he first met his best friend.

"EXPECTO PATRONUM!" A silvery white stag burst out of the end of his wand. The Dementor stumbled back.

"Well done, James! On your very first try, too! I knew you were gifted the moment I saw you," said Barten heartily. "Sirius, do you want to try?"

Sirius had been wondering what his happiest memory was.

The first time, he concentrated on the memory of the day when he was finally strong enough to leave his family. But nothing happened. He once again went into a daze of his worst memories.

"Sirius!" James was shaking him.

"Yeah?" asked Sirius in a disoriented manner. He found that he was back inside the ring of Barten's Patronus.

"Don't worry, Sirius. Even most over-age wizards can't do this spell. You'll learn. Want to try again?" said Barten.

"Yes," said Sirius determinedly, mortified at his failure, probably his first time.

This time Sirius concentrated on his first Hogwarts' train journey, when he had met James—who changed his life—because if it had been anyone but James, he would still be a depressed wreck over his family, alone and helpless.

A silver dog burst out of Sirius' wand and repelled the Dementor.

"You did it, mate!" cried James excitedly.

"Remus, go," said Professor Barten.

But Remus just couldn't do it. No matter what memory he thought of—the day Sirius, James and Peter became his friends, or the day he became a Prefect, or the day he got his OWL result—every time he faced the Dementors, the werewolf memories would hit him hard, like physical pain, and he would crumble.

"It's all right, Remus," said Barten, after Remus failed for the sixth time. Remus was still white faced inside the Patronus ring. "I understand it is harder for you than for others."

As Peter went out, Sirius slung an arm around Remus' shoulders and James patted his arm.

Peter gave up on the first try and fled back to the safety ring.

They thanked Professor Barten, who gave Remus another time next week, and returned to the common room.

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After three weeks, Remus was beginning to realize that he would never learn the Patronus charm.

"Why can't I do it?" he cried to his friends in the dormitory one night.

"That's easy—your worst memories are a lot worse than ours, Moony," said James.

"And don't worry," said Sirius. "We'll always be together—the four of us. If Demetors attack, we'll protect you—me and James.'

"I know you will, Padfoot," said Remus; his despair had already subsided.