When the bell rang, Taylor hung back, staring at me with a look of concern.

"Jessa," she said. "Are you all right? You look like you've seen a ghost."

I waited until Lana was out of the classroom before turning to Taylor. "Something is wrong with me," I hissed.

"What are you talking about?"

"I can't remember Lana. At all."

Taylor's eyes narrowed and she rolled up the sleeves of her canvas jacket, as if ready to delve into some detective work. "What do you mean you can't remember her?"

"I mean that every memory I have in my head is telling me that Lana Gibbons did not go here until today." I gestured to the seat she had been sitting in. "That seat has been empty all year, I'm sure of it." I then pointed to my friend. "And I could have sworn that at your birthday dinner, it was just the three of us. Me, you, and Sam. That's it. But she's in the picture on Facebook!"

"Umm... well, I hate to break it to you, but she definitely was at my birthday. So I... uh, I'm not really sure what to say to you. Except that this is really weird."

"I know," I said with a groan. "Do you think there was something in the muffin? How can I have just entirely forgotten one person?"

"Look," Taylor said, gently tugging my arm until I got to my feet. "Let's go to our next class. You're probably just tired or having a brain fart. I bet you in like five minutes you're going to remember who she is, which means you're worrying for no reason. Plus we have that Calc test today—you can't miss that. You know Mr. Allen makes the make-up tests harder."

"Well," I mumbled, "let's hope that I don't forget how derivatives work before third period. If I do, I'm screwed."

Taylor laughed. She had the best laugh out of anyone I knew; it was infectious and put a grin on my face despite the situation. "If you forget that, I'll personally bring you to the nurse myself. Oh, and also—" She bent down and grabbed the paper bag. "If you're not going to eat the rest of this, I will!"

I smiled. "Fine," I said, letting her lead me out into the hallway.

However, the grin fell off my face as soon as I stepped out of the classroom. Lana Gibbons was leaning against a nearby locker, chatting with another one of our classmates—Billy Stevens, a boy on our lacrosse team. I stared at Lana's face, trying to will it into my memory, but I was still coming up blank. In fact, the more that I stared at her, the more I was convinced that she didn't exist at all.

Lana wasn't in my AP Bio class, but she was in math with us. And this time, she sat right in front of me. Her black hair tickled my desk as I wrote my name on the top of my test.

I should remember seeing her hair on my desk, I thought as I dated the page, and yet in my memory, that seat had always been empty. In fact, I distinctly remembered propping my feet on it just last week and getting in trouble with Mr. Allan.

Luckily, my calculus skills hadn't vanished, and I survived the test without too much emotional scarring. It was nice, in a way. Solving the derivatives and drawing out graphs took over my mind for a bit, blocking out thoughts of this girl. But as soon as Mr. Allan called time and I passed my exam to Lana, the paranoia crept back in.

"I'm not going to make it through this day," I muttered to Taylor as we took the stairs together down to the South Cafeteria.

"Yeah that exam was brutal." She blew out, her brown bangs ruffling from her breath. "I totally messed up that last graph question."

"I meant the Lana thing," I said. I could see Lana up ahead, chatting with Sylvia Capstone, head cheerleader. But a few seconds later, she slipped away from Sylvia and sidled up next to a short guy trying his best not to be seen: Peter Thatcher, the nerdiest person in the whole school.

What the...

"Who does she hang out with?" I asked.

"Who? Lana?"

"Yes, Lana."

Taylor paused, thinking about it. "She floats around a bit. I don't think I've ever seen her eat lunch with the same people twice."

That's weird, I thought. Arlington High School was not a particularly cliquey place, but sitting with a completely new group of people every single day? That was odd—particularly for someone as attractive as her. Being nice was one thing, but jumping from the head cheerleader to class nerd within seconds? Who did that?

"I think I'm going to call my mom to pick me up during her lunch break," I said to Taylor as we finally entered the cafeteria. "I'm too freaked out. Maybe you're right and I just need a nap. But what if I have a brain tumor or like, teenage dementia? Maybe I should have my mom make me an appointment with a psychiatrist or a neurosurgeon or something."

Taylor grabbed a seat at our favorite table by the glass sliding doors. "No, I get it. It must be freaky for you to not recognize her."

I nodded and pulled out my lunch bag. "Tell me about it."

As I unwrapped the aluminum foil hiding my turkey sandwich, a voice from above asked: "Mind if I sit with you guys?"

I didn't recognize the voice—which meant that I knew exactly who it belonged to.

Lana Gibbons.

I turned my head and saw her standing beside us, lunch tray in hand. Her fitted blouse hugged her chest. Her long dark hair cascaded over her shoulders. And her nails were filed and painted a dark purple.

"Hey," Taylor said, gesturing at the empty chair. "Go for it."

My heart was pounding wildly in my chest as she sat down. Up close, she looked even more illusory: less like a human and even more like a figment of my imagination. "Hi Lana," I said, trying to sound casual and not entirely succeeding. My stomach felt large and bloated, as if someone had pumped it full of air.

Lana frowned as she looked at me. "Jessa, are you all right? I saw you stay late in Gov this morning."

"Yeah, I'm just not feeling well," I said.

"Actually," Taylor interjected, biting into her sandwich, "this is going to sound so crazy, but Jessa can't remember you."

Lana raised an eyebrow and I shot Taylor a dirty look. I hadn't expected her to spill the beans. But now that she had, I realized that I wasn't angry or embarrassed. She had stated the truth: I couldn't remember Lana. And it was really, really bothering me.

So I turned away from my friend and looked this new girl straight in her eye. I tried to still my shaking hand and nodded. "She's right. Something's going on with my memory. And the only thing I can't seem to remember is you."

Lana's eyebrows furrowed in concern, but my stomach's churning only intensified. I had the strongest feeling that beneath the surface, Lana was smiling at me, triumphant. "Well," she said, "maybe I can help jog your memory. I'll swing by your house tonight, after school?"

"Er, well my mom..."

I started coming up with a lie—all I wanted to do was lie down and sleep this thing off—but my phone suddenly buzzed. When I swiped, I saw a text message from my mother: Hey honey! I just finished making a batch of cookies today and it reminded me of how much Lana liked them when she was over last week. You should have her swing by today to pick some up.

My palms started sweating. This was all getting too creepy too quickly, and I didn't know what to do. So I did the only thing I could do.

I said, "Sure."