Libby Nichols arrives in London with a broken heart and her life in shambles. The first person she meets, the elderly Frank, tells her about an incident that happened in 1962, when he met a girl on bus number 88, who had beautiful red hair, just like Libby's. They had arranged to meet at the National Gallery, but he lost the ticket on which he had written her phone number.
Since then, he takes the same bus every day hoping to find her. However, his efforts are fruitless.
Enthralled by the story, Libby takes action and, with the help of an unexpected friend, puts up posters along the entire bus route. She begins to overcome her reservations, makes new friends, and opens herself to a new romance. But with Frank's dementia worsening, the chances of finding the girl from bus 88 are dwindling...