The first time Alice Fancourt goes out after their daughter is born, she leaves the two-week-old infant with her husband, David. When she returns only two hours later, she swears the baby in the crib is not her child. Despite her distress, David is adamant that she is wrong. The police are called to the scene. Detective Constable Simon Waterhouse is sympathetic, but he doubts Alice's story. His superior, Sergeant Charlie Zailer, thinks that Alice must be suffering from some sort of delusion brought on by postpartum depressions. With an increasingly hostile and menacing David swearing she must either be mad or lying, how can Alice make the police believe her before it's too late?