This is true— no lie. Summer before college, 3 AM. I'm in bed texting my BAE Sammy, and he forgets it's our four-month anniversary.

I'm like, "WTH ya dip."

Sammy texts, "JK."

"Whatever."

Then he's all, "Sorry I luv u brainy gurl letz meet up."

I'm bored and on board. Haven't slept three hours straight in months, and I'm full of that achy feeling again, the kind that infects your wrists and makes you wanna bend 'em back 'til they snap off.

And Sammy's stupid, but he has those big puppy eyes too, and he smells like fresh dug earth and spicy soap and sea spray cologne. I got feels for all that tonight.

I get my fleek going, then sneak past my stepdad's room. The smell pluming through the door-crack tells me he's been praying to St. Blaze.

I'm in my PJs and best kicks. Chilly, so I pull on the Caltech swagshirt I got from orientation last month. Lit, still can't believe it— full ride to Caltech. Stepdad thought it was a mistake. Maybe it was.

I step out, breathe in the night. Half moon's up, like a cookie with one big bite out. Air's tingly, like anything might happen.

I hear a cat scream somewhere, not a please-screw-me scream, but an I'm-totally-screwed scream. I stop, nearly turn around to help it, but naw, Sammy's waiting.

The sidewalk's torqued, the streets empty— I'm skeeved. No movies or bowling allies here. Old tires on overgrown lawns, even some wanna-be teen gangs.

I walk faster.

Can't wait to flee this garbage town. School creeps called me the 'math-a-ma-bitchin.' Online calculus in eighth grade and perfect math boards put me on square one of everyone's burn list. But know what? I'm getting out and they're not. I'm going to Cal-effing-tech. Blaze that, stepdad.

My boy'll be in the abandoned mall's parking lot by the boarded-up arcade, and he'll be handy, but that's okay. Sammy chases the achy feelings away. I clench my fists and move my wrists as far back as they go. Barely helps.

I round a corner and someone's there— just there. She's my height, has my hair, my face, my Caltech swagshirt— only it's worn and faded.

She says, "Turn around. Go home."

I'm like, "Who the hell are you?" But I already know.

She smiles. "I'm just the integral of my life over all my choices. Like anyone else."

Yeah, that's something geeky I'd say. "I thought this was impossible."

She touches her hair with one hand and mine with the other. "Well, it is possible, brainy girl, and you'll solve the crap out of it in ten years, so here we are. Now go home."

I let her words bubble through me.

That cat cries again —we both turn our heads the same way— she's worried about it too.

I say, "Well, old-me, what happens if I go? Does Sammy hurt me?"

She shakes her head. "Sammy's a dumb ass, but he's not that guy."

I shift from side to side— achy feeling's getting worse. "So, what does happen if I go meet Sammy?"

Now she looks worried, and she bends her own fists backward. "It's over."

"I die?"

"Yeah."

I'm tops at math, but this equation throws me. "Old-me, how'd you get here? If you don't show up, I go to Sammy and die. So how do I come back and warn myself? This is bull." I start to march past her.

She throws up an arm to stop me: her wrist has the kitten-playing-with-yarn tattoo I almost got last summer. "Young-me, there's more than one chronline. The machine surfs chronlines like radio channels. Sometimes you don't go to Sammy, even without a warning. That's what happened when I was you."

"You surf chronlines, saving the young-yourselves who go to meet Sammy?"

She nods. "Gotta save my girls. Poor little kittens."

She still hasn't said what happens— she's avoiding something. "Sammy dies, doesn't he?"

She holds her breath.

"I have to save him."

"Too dangerous."

"I'll text him, warn him."

"Doesn't work."

I swipe my phone, start to type. No signal.

She puts her hand over my phone screen, looks at me, seems so sad.

Shots crack in the distance.

She says, "He didn't suffer."

I cry out, think of his puppy eyes. She knew I'd try to save him, no matter what. She delayed me on purpose.

She tries to hug me; I break it off.

I grab her by the shoulders. "Use the machine to save him. Go back to before—"

"Can't. The channels dance around; I'll never find this chronline again."

I thump on her shoulders with both fists, blind with tears. "You could have tried harder. You could have saved us both. I'll never forgive you."

She grabs my wrists, squeezes hard in the right places, snuffs the ache.

She says, "You're right about that, because I'll never forgive myself. It's possible to save him, but it's risky, so I don't try."

I step back. "When I get to be you, I won't be a coward."

She puts a hand to her mouth, squeezes her eyes shut.

I'm shook but wonder something. "You didn't get warned, so why'd you blow off Sammy when you were me?"

The cat screams again.

She points toward it, starts to dissolve.

She never loved Sammy; she chose the cat over being with him. The integral of my life over all my choices isn't equal to hers— so, she's not me.

I'll save Sammy someday. I'll study harder, be smarter, figure out the dancing channels. I'll take the risk.

I'll save him. No lie.

Wrecked, I turn to rescue the damn cat.