A sudden warmth grew in my jacket pocket.

I reached in and pulled out my father’s portable monitor.

The screen had turned itself back on.

The blue light illuminated the interior of the car.

A small map was displaying on the screen, showing a blinking red dot.

The dot was positioned exactly where we were on the highway.

“Mara,” I said, holding up the screen.

“What is that?” she asked, her eyes darting to the display.

“It’s a locator map,” I said. “It’s showing our coordinates.”

“How is it getting a signal?” Mara asked. “The satellite link should be passive.”

A text box popped up over the map.

It was another message from Caroline.

“You always did have your father’s eyes, Natalie,” the message read. “But you inherited my phone.”

I looked down at the casing of the monitor.

Near the base of the antenna, a tiny green light was blinking in a steady rhythm.

“The device,” I said. “It’s broadcasting.”

“Shut it down,” Mara said, her voice rising.

I pressed the power button, but the screen didn’t fade.

“It won’t turn off,” I said. “The software is locked.”