The report came through a minute later. As soon as I got it, I scrolled down to the bottom and looked at September 9. The text in question was the only entry for that day.

It had come into Zoe’s phone at 8:05 a.m., right in the middle of Branaff’s homeroom period. That was also about fifteen minutes before Ethan and Zoe disappeared.

It took me only a few keystrokes to run a reverse lookup on the incoming phone number. It was registered to a Cathy Allison, with an address in Foggy Bottom. And in fact, I knew the exact house. I’d been there on Saturday to interview Ms. Allison’s daughter Emma, one of Zoe’s inner circle of girlfriends.

I looked up at the clock. It was 10:15 a.m. Emma would be in class right now — third period.

If I left right away, I could be there by fourth.

EMMA ALLISON’S EYES went wide as she stepped out of the science lab and into the hall, where I was waiting for her. So was the headmaster.

“Emma, Detective Cross is here to ask you a few questions,” Mr. Skillings told her.

She seemed like a scared little girl to me, but in a fourteen-going-on-thirty kind of way. She had too much dark liner around her eyes and a pair of half-shredded leggings under her school uniform. The thick-soled boots looked just like the red ones Zoe had been wearing the morning she disappeared.

“Did they find Zoe?” she blurted out. “Oh please. Please, please, please.”

“No, I’m sorry, Emma,” I said. “Actually, what I need is to get a look at your phone.”

“My phone? But why? What’s going on?”

“Do you have the phone with you?”

“I hope not,” Skillings said pointedly. “The students aren’t allowed to have any electronics in class. Isn’t that right, Emma?”

“It’s in my locker,” she said.

The headmaster motioned her up the hall, not even trying to hide his impatience. I’d already spent a good fifteen minutes in his office, tracking down Mrs. Allison and getting permission to speak with Emma in the first place.

We followed her outside and across a breezeway, into one of the campus’s several redbrick annex buildings.

Halfway up another hallway, Emma stopped at locker 733 and twirled the combination on the lock.

She reached inside, took out an iPhone in a zebra-striped rubber case, and held it out for me.

Her eyes flared again when I pulled on a pair of latex gloves to take it from her.

“Emma, when we spoke on Saturday, you said that the last time you had any contact with Zoe was the afternoon before the kidnapping. Is that right?” I asked.

“Yeah. We have eighth period social studies.”

She craned her neck, trying to see what I was doing. I’d powered up the phone and navigated over to her Sent messages.

Sure enough, there it was, September 9, 8:05 a.m.