The Greystone kids thought they knew. Chess has always been the protector of his younger siblings, Emma loves math, and Finn does what Finn does best—acting silly and being adored. They’ve been a happy family, just the three of them and their mom.

But everything changes when reports of three kidnapped children—who share the same first and middle names, ages, and exact birth dates as the Greystone kids—reach the Greystone family. This bizarre coincidence makes them wonder: Who, exactly, are these strangers? Before Chess, Emma, and Finn can question their mom about it, she takes off on a mysterious work trip. But puzzling clues left behind lead to complex codes, hidden rooms, and a dangerous secret that will turn their world upside down.