“I was just wondering.” High up, a piece of moon was showing through, not yet brighter than the sky. “Did you know,” he said, changing the subject, “that all the water in the world is all there will ever be?”

“Meaning . . . ?”

“Meaning that water is constantly turning from one state into another. Ninety-seven percent is in the oceans. Only three percent is fresh. There’s surface water, there’s ground water underneath, there’s what’s stored in ice and snow and in the air—”

“In the air?”

He made his lips a circle and blew. “Breath is mostly water. We’re made out of water. But the thing is, there’s a fixed amount. It can’t be added to or taken away. It just changes into another form.”

“Okay . . .”

“We drink the same water the dinosaurs did.”

“Okay. So when the earth heats up four degrees,” I said, “and the ice caps melt and the trees and animals die, the water in them eventually ends up in the oceans?”

“And the air.”

I thought for a minute. “Is that comforting? I don’t know if that’s very comforting.”

“It is, in a way. In the long run.”

The lake looked strange all of a sudden, as though the trees had turned to liquid and the water to rock. I wanted to smash its shiny surface. I did an experimental hoot, like you do to test an echo, and something took the sound away from me and stretched it out into a scream. Every awful thing that had ever happened to me, everything I was furious with or desperate about, got sucked into the scream, and it got louder and louder like a siren getting closer and closer, until it filled the sky, scaring even me.

“What the—!” shouted Jack.

“Sorry,” I said cheerfully. Let him think that screaming at the lake was something we did all the time, just for fun.

He was staring at me, not sure whether to laugh.

“You know what, Jack? I could end up raining on you. Or in your bathwater.”

“Maddy . . .”

“Coming out of your faucets. I could end up in your coffee. Not that you would know it was me.”

“Anything is possible,” he said in a weak voice.

“Or maybe you would know.”

We were silent for a long time.

“Jack?” I said at last.

“Yeah?”

“I want to still be somewhere.”

His retort was instant. “They can do amazing things. They know so much these days! Don’t talk like that, Maddy. Please.”

I noticed that the more worked up Jack got, the calmer I became. Maybe there was only a certain amount of fear to go around, so we took turns holding it.

“Just say it does happen. Just say. Wouldn’t it be sad if you and I never talked about it?”

I had never seen him look so scared.

“Jack?” I said. “Don’t take this the wrong way.”

“Okay.”