“Mamma Mia! Here We Go Again” finds the young woman with three fathers (Amanda Seyfried as Sophie) about to realize her mother’s dream of a luxury hotel on the idyllic island of Kalokairi (the Greek island of Skopelos in the original, in this one the Croatian island of Vis, which gave the production tax breaks).

It is bittersweet because her mother (Meryl Streep as Donna) has died. She and her step- and one of three possible biological fathers (Pierce Brosnan), conveniently an architect, miss her dearly. “It will get better,” she reassures him. “Yes, just not quite yet,” he answers. Working on the grand opening party makes her feel closer to her mother. But she also misses Sky (Dominic Cooper), who is getting training in hotel management and has been offered a dream job half a world away. She also wishes her other two fathers could be there for the opening, straight-laced British lawyer Harry (Colin Firth), who is negotiating a big merger in Japan, and Bill (Stellan Skarsgård), who is getting an award for being Sweden’s greatest person because this movie does not really care enough about minor details to Google an actual award or invent a plausible one. And why should it? This is a movie that asks us to believe Cher is Meryl Streep’s mother. And that someone could have a daughter in 1980 who would still be in her early 20’s.

While Sophie is planning “the most incredible party of all time,” the primary focus of the film is on filling in the dot, dot, dots of Donna’s origin story, from her college graduation in 1979 (the math does not really add up here, either), her friendship (and performances) with Tanya (Jessica Keenan Wynn as the deliciously acerbic younger version of the character played by Christine Baranski) and Rosie (Alexa Davies as the younger version of the tender-hearted character played by Julie Walter), and her encounters with Bill, Harry, and Sam (younger versions played by Josh Dylan, Hugh Skinner, and Jeremy Irvine).

Lily James (“Baby Driver,” “Cinderella”) plays the young Donna, wearing gold platform boots under her graduation gown as she strides to the podium to give the graduation speech, then tosses off the gown to reveal a wild mash-up of a costume that could only be found in an ABBA performance or perhaps on display at the Bad Taste Museum in the Hall of What Were They Thinking. Her friends join her on stage for a jubilant performance of “I Kissed a Teacher,” and then bid her farewell as she embarks on her adventure. In France, she meets a shy Englishman. It is Harry. In one of the movie’s highlights, they sing and dance to a rousing “Waterloo” in a restaurant. She next meets Bill, who gives her a ride on his boat

And then she meets Sam, who wins her heart and then breaks it. By then she is pregnant, and by then she knows that this island is where she wants to make her home.

There is more skill in the crystalline harmonies, rock star poses, screen saver vistas, and segues between time and space than in the storyline, which is both too sad and too silly. Pierce Brosnan still can’t sing. The script often sounds like it was badly translated from the original Swedish. But it’s a cool treat on a hot summer evening, and let’s face it — you couldn’t escape if you wanted to.

NOTE: Wynn is the latest in five generations of one of the most luminary of show business families, including actors Ed Wynn (“Mary Poppins”) and Kennan Wynn (“Dr. Strangelove”) and writer Tracy Kennan Wynn (“The Longest Yard”). And of course, be sure to stay through the end credits for a final musical number!

Parents should know that this film includes sexual references and non-explicit situations, questions of paternity, some sexual humor, childbirth scene, some mild language, and some alcohol.

Family discussion: How do you bolster your friends and family? What makes your soul shine? How do you make a complicated problem simple?

If you like this, try: the first “Mamma Mia” and “Walking on Sunshine” and read Susan Wloszczyna’s interview with Judy Craymer, who came up with the idea of turning ABBA’s songs into a play.