When Alice Fancourt leaves her infant daughter at home with her husband David for the first time since becoming a new mother, she returns to a horrifying sight: her daughter, Florence, has been swapped with another baby. In hysterics, Alice rushes to call the police, but soon discovers that no one - not even David - believes her. When the police are called in, Detective Simon Waterhouse is drawn to the lovely Alice but doubts her story, while his boss, Charlotte "Charlie" Zailer thinks the whole case is a waste of time. But one week later, both Alice and the baby have disappeared...