Page 124 of The Chain

Marty answers immediately. “Yeah, she’s fine, we’re just finishing up at the mall,” he says.

“You have her in your line of sight?”

“Yeah, of course. She’s at the Adidas store with Stuart.”

“And then you’re going to Ginger’s dad’s house?”

“Grandfather’s house. What’s the matter, Rach? I can tell something’s up.”

“I just want to know that Kylie’s safe.”

“She’s safe. Ginger’s twin brother will be there, and Ginger is an actual card-carrying FBI agent, and her grandfather is ex–Boston PD. I can’t think of much safer than that.”

“That’s good, Marty. Keep her safe, OK?”

“I will, sweetie. You take care now. Take it easy this weekend, for God’s sake. You need your strength, okay?”

“I will.”

They say goodbye and hang up.

“What now?” Pete asks. “The cops?”

Rachel ties her hair back in a ponytail. “Kylie’s safe but they are going to be coming for us. We need to get out of this house.”

“What’s the plan?” Pete asks.

“We download the app, see if it works. If we can find them, we’ll locate their residence and call the police.”

“And if we can’t?”

“We call Ginger and tell her everything and ask her to take Kylie into protective custody. Then I guess we turn ourselves in.”

Pete looks at her. “How long do you think we have?”

“I don’t know. Hours? Let’s get started,” Rachel says.

She turns on Erik’s app. It has downloaded successfully but when she tries to open it, a message flashes on the phone’s home screen:For this app to work you need to enter the next number in this sequence: 8, 9, 10, 15, 16, 20…If you enter the wrong number your phone will be locked and all devices associated with your account will be disabled for twenty-four hours.

Rachel shows the message to Pete.

“That is a powerful bit of tech. We need the exact digits or we’re screwed,” Pete mutters.

“What about the number pattern? Recognize it?”

He shakes his head. “It’s not prime numbers. It’s not the sum of the numbers before. It’s not any series that I know of offhand.”

“We get only one shot at this. If we mess this up, we won’t be able to get back in until tomorrow.”

“And tomorrow will be too damn late.”

“Eight, nine, ten, fifteen, sixteen, twenty,” Rachel says aloud.

“I’ll Google it,” Pete says, but all he gets are links to YouTube videos teaching kids how to count.

Rachel closes her eyes and tries to think. What sequence is this? It’s something she has seen before somewhere.

“An additional security protocol makes no sense at this stage, does it, Pete?” she says, thinking out loud. “I mean, Erik knows that the only person who is going to download this app is me. Right?”