At the age of 21, Tim Lake discovers from his father that the men in their family have the supernatural ability to time travel within their own lifespan, with the simple act of clenching their fists in a dark place. Secrecy is a strict rule—they cannot share this gift with anyone else. After initially using this power to improve his life in small, personal ways, such as redoing embarrassing social encounters, Tim decides that he will use his ability to find true love. This aspiration leads him to move from his Cornwall family home to London, where he pursues a career as a lawyer and begins his quest.

In London, Tim meets Mary, a charming and insecure young woman with whom he forms an immediate connection. Through a series of time-traveling missteps, he finds his time with her erased by his own interventions, forcing him to meet and win her over repeatedly. As their relationship grows, Tim continues to use his gift to create what he believes to be the perfect scenarios for their love to flourish. However, he soon begins to learn the complexities and limits of his time-traveling abilities, as each change in the past has unforeseen impacts on the present.