Five years ago police psychologist Martin Schwartz lost his wife and son. They were holidaying on a cruise ship when they simply vanished, the case written off as a straightforward murder-suicide. They are not the only parent-and-child pair to have disappeared from the ship in recent years – and yet, the authorities seem unconcerned. But when a missing girl reappears – carrying Martin's son's beloved teddy bear – the police won't be able to avoid the truth that something sinister is lurking on board...