Agatha Christie, in London to visit her literary agent, is boarding a train, preoccupied with the devastating knowledge that her husband is having an affair. She feels a light touch on her back, causing her to lose her balance, then a sense of someone pulling her to safety from the rush of the incoming train. So begins a terrifying sequence of events--for her rescuer is no guardian angel, rather he is a blackmailer of the most insidious, manipulative kind.