"In her enthralling debut, Gilly Macmillan explores a mother's search for her missing son, weaving a taut psychological thriller as gripping and skillful as The Girl on the Train and The Guilty One."--In a heartbeat, everything changes ... Rachel Jenner is walking in a Bristol park with her eight-year-old son, Ben, when he asks if he can run ahead. It's an ordinary request on an ordinary Sunday afternoon, and Rachel has no reason to worry--until Ben...