Lara Finch is living a lie. Everyone thinks she has a happy life in Cornwall, married to the devoted Sam, but in fact she is desperately bored. When she is offered a new job that involves commuting to London by sleeper train, she meets Guy and starts an illicit affair. When Lara vanishes from the night train without leaving a trace, only her friend Iris disbelieves the official version of events, and sets out to find her. For Iris, it is the start of a voyage that will take her further than she's ever travelled and on to a trail of old crimes and dark secrets. For Lara, it is the end of a journey that started a long time ago. A journey she must finish, before it destroys her...