On the fictional Greek island of Kalokairi (Greek for 'Summer'), bride-to-be Sophie Sheridan reveals to her bridesmaids that she has secretly invited three men to her wedding without telling her mother, Donna: Irish-American architect Sam Carmichael, Swedish travel writer Bill Anderson, and British banker Harry Bright. One of the three is Sophie's biological father, though she doesn't know which, and she wants him to give her away at the wedding; she believes that after spending time with each of them, she will learn who fathered her.

When the three men arrive at Kalokairi, Sophie explains she sent the wedding invitations, not Donna, but does not reveal that she believes one of them is her father. She hides the men in Donna's goat house, and they hesitantly agree not to reveal themselves yet, as it is a surprise.

As Donna is working on the goat house, she spies on them. Dumbfounded…