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

They didn’t even seem to notice us, they were so busy blinking and flexing their arms and their legs. We moved as quickly and quietly as we could, looking for Emily and Jacob. We found them sitting on one of the benches. Emily was dialing frantically on her phone, and Jacob was sitting there next to her, his arms clasped around his legs.

Adam lay my mother on the ground next to the bench, near the base of a scrawny palm tree. Jacob sat next to her and held her still hand. Adam was out of breath, and he wiped his sweaty face. I realized—it wasn’t just that she was heavy. We were getting weaker. My mom lay on the ground, a terrible silvered color.

“Did you reach Phoebe?” I asked Emily.

She shook her head no. “I’m calling the airport,” she said. “I’m waiting for them to page your grandmother.”

“The equation was something my dad wrote down,” I said fast and low, to Emily and Jacob. Adam’s eyes were closed. His lips were moving like he was praying. “He said, if a genocide was unsuccessful, it meant that someone had tried to stop it. And then the contrapositive—.”

“The contrapositive is that, if no one tried to stop it….” Emily looked up at the shadows, and paled. “Then it was successful, I guess.”

“Yeah,” I said.

“What are we supposed to do? I can’t reach Phoebe.”

“I’m sorry,” I said.

“What?”

“I’m sorry about, you know—that I said I would give them the answer. Or whatever it was.” I swallowed hard. “I—well I want to say I wouldn’t. I hope I wouldn’t have. But it was wrong, that’s all, and I’m sorry.”

She nodded, and shrugged. “Yeah, well OK, but.” She looked up at the shadows, who had clumped together in the basketball court. “I don’t know that that’s going to help.”

“We have to do something,” I said.

“I know,” Emily said. “I’m just trying to think what.”

I bent down next to my mom, close to her face.

“Mom. Mom.”

Her eyelids fluttered and then opened. The sky was reflected in her eyes. “We’re outside,” she whispered.

“OK, Mom,” I crouched close to her so she would hear how important it was. “You understand Dad’s equation. Mom—how do we stop them?”

She turned to me and she smiled, this beautiful tired smile. “Oh Alyssa! You just have to be good, honey.”

“Like what? Be nice to them? Mom? Is that what was on the thing that Phoebe was bringing? MOM?” Her eyes fluttered shut, and I turned fast to Adam and Emily. “Is the airport answering?” Emily shook her head. She was pale, and scared, and getting to her feet.

“Alyssa!” We all looked up. There, walking into the park, were my grandmother, and Doris, and Pinky, and Phoebe, who had called out, and was walking her bicycle with one hand and waving an envelope in the other.