Donna's (Meryl Streep) wild past catches up with her on the eve of her daughter's wedding. Sophie (Amanda Seyfried) is anxious to find out who her father is in order to have him walk her down the aisle. When she stumbles on her mother's journal while rifling through some old boxes, she discovers that three different men had relations with her mom before her birth. Without informing Donna, Sophie sends invitations to all of them in hopes they'll attend the ceremony and she'll be able to figure out who her dad is.
No one is more surprised than Donna when her former lovers, Sam (Pierce Brosnan), Harry (Colin Firth), and Bill (Stellan Skarsgard) all arrive on the idyllic Greek island where she runs a dilapidated holiday villa. Sworn to secrecy by Sophie, none of the men will confess why they are there. However, as the nuptials draw nearer, Sophie still can't determine which man is her biological father.
Meanwhile, Donna's friends, Rosie (Julie Walters) and Tanya (Christine Baranski) also show up for the big event. Disappointed by the changes they see in the overworked hostess, they try to rekindle Donna's carefree passion and spontaneity. Rosie, a cookbook author, and Tanya, a serial bride, don their old dancing outfits and talk their friend into putting on a performance with them at her daughter's bridal party.
Striding across a temporary stage in their platform boots and boas, the three aging friends belt out the lyrics to "Super Trouper". It's just one performance in the film that discloses the crooning talents of the actors in this cast. Set to the melodies of the Swedish singing group ABBA, this plot is propelled forward by a score of musical interludes featuring the voices of all the main characters, along with those of Sophie's fiance Sky (Dominic Cooper) and a young bartender (Philip Michael) who hounds Tanya for some sexual attention while repeatedly pouring drinks for the visitors.
For those familiar with ABBA and their music, this theatrical adaptation of the play Mamma Mia! may be an enjoyable diversion. Yet the script presents problems for many family viewers. Donna's simultaneous affairs leave her unsure as to the parentage of her child and disclosing that fact to Sophie (as well as the men she slept with) proves to be embarrassing and disconcerting. Twenty years after the fact, Donna appears to face some consequences for her activities. Still, sexual comments, bawdy jokes and discussions of former liaisons make up much of the script. Men in various degrees of undress (including male buttock nudity) are also seen.
Given the success of the play and the prospects of the film, Mamma Mia! is a testament to the idea that catchy tunes can make even questionable content more palatable. That's a tactic mammas (and papas) might find hard to swallow.