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 vanishes. Police are called, search parties go out, and Rachel, already insecure after her recent divorce, feels herself coming undone. As hours and then days pass without a sign of Ben, everyone who knew him is called into question, from Rachel's newly married ex-husband to her mother-of-the-year sister.