Jenny Bowen is going home. Boarding the Caledonian Sleeper, all she wants to do is forget about her upcoming divorce and relax on the ten-hour journey through the night.

In her search for her cabin, Jenny helps a panicked woman with a young girl she assumes to be her daughter. Then she finds her compartment and falls straight to sleep.

Waking in the night, Jenny discovers the woman dead in her cabin ... but there's no sign of the little girl. The train company have no record of a child being booked on the train, and CCTV shows the dead woman boarding alone.

The police don't believe Jenny, and soon she tries to put the incident out of her head and tells herself that everyone else is right: she must have imagined the little girl.

But deep down, she knows that isn't the truth.