*NATIONAL BESTSELLER* What happens when your worst nightmare becomes your reality? One sunny day in California, Jessie is hugging her nine-year-old son, Dylan, goodbye at the airport. He's travelling alone, all the way across the country, to visit his grandparents and father, Jessie's soon-to-be ex-husband. Her heart is breaking, but she puts on a brave face and gives her son one last wave as a flight attendant leads him away.  Several hours later, Jessie gets a frantic call from Dylan's grandmother in New York. Dylan is missing. In a split-second, Jessie's world turns upside down. The AirTag she'd put in Dylan's backpack says he's still at LAX. The airline insists that he was picked up at JFK by an elderly couple claiming to be his grandparents—but Jessie's in-laws insist they haven't seen him. Dylan has disappeared into thin air. At the same moment, miles away, in Toronto, a train operator loses control of a subway train, and the fiery crash kills five passengers and injures dozens of others. Was this a fatal human error or something more sinister? And how exactly is it connected to the disappearance of Dylan? Because, somehow, it is.