When a mysterious stranger sat down beside her on a park bench one day in the spring of 2009, Vivienne Riley was thinking only of completing her PhD dissertation in history. Soon, however, she finds herself being recruited into a top-secret experimental program designed to right some of the wrongs of the past by sending time travelers back to the Second World War to attempt to change the future. Vivienne agrees to participate and soon she is on a collision course that imperils her own life and the lives of those she loves. Over the course of her journey into the past, Vivienne finds love, suffers heartbreak, and learns firsthand what it means to live in and survive World War II in London, all the while making a series of well-meaning decisions that may alter the future in ways she cannot imagine. Is it really possible to change history, even with time travel-and even if we could, is it a good idea to try?