(Start here.) (Or just go backwards.)

We got up out of the tunnel, and opened the letter to study it. It was my mother’s crazy handwriting, and all it said was:

If A  —–>   B

If -B  —–>  -A.

Underneath was a note from Phoebe.

“I don’t know what this means, and there is all this other stuff and I AM COMING! SEE YOU SOOOOOOOOOOON!!!!

We all looked at it for a minute. “Well, it’s not math, I don’t think,” Adam said doubtfully.

“Duh it’s not math,” I snapped. They both gave me a look. I tried to press down the awful feeling of being me for a second. “Sorry. I told you: Philosophy. My mom studies philosophy. It’s—I think it’s logic.”

“I think it’s a contrapositive,” Emily said.

Adam and I looked at her. “That’s logic,” she said. “But it’s not like—I mean, it’s not like some complicated thing she discovered. We learned it in enriched math.” I tried not to snort.

And Adam said, “What does it mean?”

Emily frowned in concentration. “It’s the way they write if, then statements, and make logical deductions from them. Like, If something is an eagle, Then it’s also a bird. If A, then B. So if something isn’t a bird—well, then you know it’s not an eagle.” She shrugged. “True, but sort of useless in this situation, as far as I can tell.”

“Great,” I said. “Perfect.” I folded up the letter and shoved it in my pocket. “Look, let’s just go find Phoebe. I’m sure she’s at my grandma’s house by now, and she’ll probably have some list of whatever A and B is or something.”

Emily hesitated. “Won’t your grandmother be there? Won’t she want to, you know, talk to you?”

“It’ll be fine,” I said, because I didn’t know what else to do.

So we walked. And I convinced myself that when we got there we would see Phoebe, just sitting there leaning her back against my grandparents’ door. The closer we got, the more excited I felt, until when we reached their block I started running, even though it was so hot, and I felt weird and sick, and I look really dumb when I run. I saw the bike tire when I got halfway down the block. “Phoebe!”

And then it wasn’t her. Someone had left their bike on its side in the front yard. I stopped there, looking at it. Adam and Emily caught up to me from behind, saying, “Is it her? Is she there?” I shook my head and kicked the stupid bike’s tires. It was a sparkly old olive green thing, something Phoebe would never ride.

I walked to the door and then stopped. The door to my grandmother’s house was open—just a crack. Inside I could see things on the floor, and the table knocked over. I shoved the door open fast. I heard Pinky scream, and someone grabbed me. My head hit the wall with a sound like a cinderblock dropping.