Ever since a car accident tore her family apart, Holly has been part of a lonely-hearts holiday letter-writing club. Each December, she writes to a stranger who is also spending Christmas alone and receives a letter from another lonely person in return. The letters are anonymous, and the senders write whatever is in their heart. This year, the letter Holly receives is different; its writer, Emma, mentions a place Holly has visited. She becomes determined to reunite Emma with her estranged grandson, Jack. If she can fix Emma's family, she might also be able to fix her own. Though as it turns out, Holly might have less time to put things right than she thought.