The movie is less a sequel and more a prequel. Though it follows Sophie (Amanda Seyfried) as she prepares to have her first child, the bulk of the movie happens before the events of the previous film, which came out in 2008. Lily James plays a young Donna (Meryl Streep in the original film) who moves to a remote island in Greece, only to find herself entrapped in a love quadrangle with three men. This, as I'm sure you recall, is a major plot point in Mamma Mia! In the original film, the men were played by Colin Firth (Harry), Pierce Brosnan (Bill), and Stellan Skarsgård (Sam). In this 2017 "prequel," the suitors are Hugh Skinner (young Harry), Josh Dylan (young Bill), and Jeremy Irvine (young Sam). The trailer features a slow, a capella version of "Mamma Mia," the eternally perfect song, as well as one swell pair of overalls. (A reminder for those who haven't watched the 2008 film in a while: Meryl Streep's character Donna exclusively wears overalls.)