They walked around to the side street where the train passed school and past a large flock of birds attacking bread crumbs on the street, then crossed and entered a residential building.

“What is this? Who lives here?” Eden asked.

“Remember the creepy bird watcher guy?” Eli hit buzzer buttons.

“Ohh,” Eden said.

“What?” Marwan asked.

“I’ll explain later,” Eden said. Then to Eli: “But what if he’s not home?”

“I thought we’d just see if we can get on the roof?”

Made sense. The door buzzed open.

So they climbed to the third floor and all seemed winded. Marwan went ahead and climbed another flight and then doubled back to a midway landing and said, “We’re in business.”

He was the first one out, with Eden right behind him. The tar felt hot and sticky under her boots, and it seemed too bright up there, like the sun needed a dimmer switch. A few large pieces of equipment hummed, and some mushroom vents popped up out of the tar like, well, mushrooms.

Eden checked the time on her phone. The dismissal bell was about to ring.

A waist-high ledge bordered the roof and caused Eden’s stomach to flip when she got too close to it.

“I got you,” Marwan said. “Here.”

He knelt, holding her hand, and she knelt beside him, and they could still see over the wall. The music room was empty, but then one of the school’s janitors, whose name Eden did not know, walked in and opened a window about six inches and walked out.

“Okay, that’s weird,” Marwan said.

“Do you think he opened it … that day, too?” Eden said.

You could hear the bells of the school even across the street, which must be annoying for people who lived there. Through the windows, you could see students springing to life and exiting rooms. It didn’t take long before bodies started to round the corner, having emerged from the main entrance.

Eden used her phone to zoom in on the music room. “There’s no device on the desk.”

“Why did he open the window?” Marwan thought aloud.

“You guys,” Eli said, pointing. “Look.”

Eden followed the line of his finger and saw the device—so a new one—in drone mode, heading for the building, and felt another sort of flashback, this one to the night out in the marshes by the airport. There was no way it was that same machine, so this one would be new … and the same? Or different?

It went through the open window, landed on the desk. Eden zoomed again just as its drone paraphernalia retracted.

“What do we do?” Marwan asked.

“We wait,” Eli said. “It’s sending notifications, right? It’ll take them a minute.”