Sophie Sheridan prepares for the big reopening of her mother’s hotel, Donna, after she died a year ago. She is angry because two of her fathers, Harry and Bill, can not get to the ceremony and have problems in her relationship with Sky, who is in New York. In 1979, the young Donna just graduated from the university with Rosie and Tanya and is preparing to travel all over the world.
While in Paris she meets Harry and spends with him. The two spend the night together, but Donna leaves shortly thereafter. She later loses the boat to Kalokairi, but Bill offers to take her and along the way she helps a fisherman named Alexio. Without Donna knowing, Harry followed her to Greece, but it was too late and he sees her sad as she moves away.
Nowadays, Tanya and Rosie arrive to help Sophie with the reopening ceremony, and it shows that Rosie and Bill broke up. Sophie goes on a visit to Sam who still laments Donna’s death. Back in the past, Donna arrives on the island and, while exploring a farm, a sudden storm makes her find a frightened horse. She is trying to seek help for the horse and finds only the young Sam who comes and helps her release the horse.