1959 San Francisco. Four unrelated and disparate people - Harrison, Julia, Milo and Penny - are the sole passengers on a late night city bus, they who, along with Hal the bus driver, are killed immediately when the bus crashes in a traffic incident. Instead of being sent to heaven, their four souls end up inextricably attached to that of Thomas Reilly, born in another vehicle involved in the traffic incident at the moment of their deaths. Their four souls, their human form which are visible to Thomas and Thomas only, end up being Thomas' guardians, who arguably have more of an affect on his life than any human. But when their presence in Thomas' life, which manifests itself to the living world as Thomas' imaginary friends, begins to cause socialization problems for him when he is seven years old, they decide it may be best for them to become invisible to him, basically disappearing without a trace, albeit being with him in spirit unknown to him. A distraught Thomas ends up feeling abandoned by the four "people" who were his best friends. Fast forward to present day, thirty-three years after the accident. The four just learn, what they were supposed to have been told years earlier, that their purpose for being with Thomas was to tie up loose ends in their respective human lives before they are sent to heaven, and their souls transferred into the body of another creature to be born, their souls which are now required. Thomas was suppose to help them in their tasks. They were also previously unaware that they could take over Thomas' body in the process. Harrison's loose end is singing in public, he who wanted to become a professional singer, but whose stage fright always got the better of him. Julia's is telling her boyfriend John that she loved him, she who kept pushing him away in her own insecurities. Milo's is to return some stolen materials - his last job in a career as a thief - before he went straight. And Penny's is to ensure that her three children ended up being safe and together, which was not a certainty as she was a single mother without any other family. They have to reenter Thomas' life and get him to help them, which may not be easy due to his feeling of abandonment by them at a formative point in his life. That abandonment has manifested itself in Thomas having commitment issues, such as with his longtime girlfriend Anne, since he doesn't ever want to feel like he did when he was seven. And even if they can get Thomas to help them, they don't know how much time they have before they are required in heaven, and thus whether their missions can be accomplished, especially as Thomas has his own human life to lead, which not only includes trying to keep Anne in his life without making that commitment, but also his banking job where he is tasked more often than not in business foreclosures. But one will learn that their mission may not be quite be quite what it appears on the surface.