Vivi Palmer knows what it's like to live life carefully. Born with a heart defect, she was given a second chance after a transplant, but has never quite dared to make the most of it. Then she comes face-to-face with her donor's mother, Grace, who wants something in return for Vivi's second-hand heart: her help to find all the other people who have tiny pieces of her son. Reluctantly drawn into Grace's mission, Vivi tracks down a small group of strangers. And as their lives intertwine she discovers a whole new world waiting for her.