Fourteen-year-old twins forge an unlikely—and unsteady—alliance with a bitter runaway when all three find themselves being hunted. But why, and by whom? And how does the mysterious book, The Countdown Code, fit in? Over the course of this richly layered story, readers will solve puzzles and unravel codes along with the teens as they face kidnapping, medical experimentation, and AI running amok—eventually realizing that their longevity-obsessed enemies aren’t the only ones hunting them.