Yes, I know the “Mamma Mia” movies are deliberately near-campy, candy-colored fluff, played for broad laughs and easy sentimentality, with plot developments dictated by the lyrics of bubblegum hits by Abba.

Still. These movies are NUTS.

Consider both the “original” film from 2008 (based on the 1999 stage musical) and the sequel are set almost entirely on the fictional Greek island of Kalokairi (the real island is Skopelos, in the Aegean Sea) — and yet the only Greek characters are very minor supporting players/caricatures — a silent old woman carrying a load of branches on her head; a tough bar owner who is also apparently a midwife; an over-the-top romantic who gesticulates wildly and nearly drowns trying to prevent his true love from marrying the wrong man.

Then there’s the curious casting of all those Actors of Distinction Not Known for Their Singing. Pierce Brosnan (!), Stellan Skarsgard (!) and Colin Firth (!) return — and sorta sing, and kinda dance — as the three dads to Amanda Seyfried’s Sophie. And this time around Andy Garcia (!) joins the cast as, yes, Fernando.

If you’ve ever wanted to see Pierce Brosnan, Colin Firth, Stellan Skarsgard and Andy Garcia participate in a lavish musical number while wearing shiny, ’70s-themed costumes, congratulations: this is your movie.

Then there’s the scene where Skarsgard sports terribly unconvincing makeup and padding to play his own twin brother in a scene thousands of miles and planets of relevance removed from the goings-on back at the island. Oh, and there’s the much-ballyhooed addition of the fabulous Cher, who is three years older than Meryl Streep but is playing the mother of Streep’s character.

So much head-scratching madness in one corny, old-fashioned musical that hops back and forth between the late 1970s and present day, with only the thinnest of storylines holding it altogether.

And yet it’s impossible to work up anything approaching major disdain for “Mamma Mia 2,” because it’s harmless and it’s silly and it’s good-natured, and all those veterans are such gamers, trying so hard to have a good time. (They’re like the dads and uncles in those viral videos of wedding receptions and anniversary celebrations that surprise everyone by breaking out the dance moves they’ve been secretly working on for the last month.)

WARNING! SPOILERS AHEAD!

“Mamma Mia 2” picks up five years after the events of the original, in which Seyfried’s Sophie, unbeknownst to her mother Donna (Streep), invited each of her possible fathers, Sam (Brosnan), Bill (Skarsgard) and Harry (Firth) to her wedding to Sky (Dominic Cooper) in the hopes of determining which of them is her biological dad. (Twenty years earlier, Donna had trysts with the three men, who then disappeared from her life. That sounds more like the makings of a Tennessee Williams play than the setup for a musical romp, but there you have it.)

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I feel it’s OK to reveal the following because we learn it right off the bat: Donna is dead. Yep: dead. We’re never told how Donna died, which seems like a glaring omission. Was it a long illness? A tragic choreography mishap during a late-night rendition of “SOS”? WHAT HAPPENED TO DONNA?

All we know is it’s been a year since her passing, and now Sophie is about to re-open Donna’s Greek island villa in Donna’s memory — but there are all sorts of complications, from a possible relationship-ending fight with Sky to an impending storm to the absence of Harry and Bill to the fact we already heard virtually all of Abba’s hits in the first movie. So, in addition to relatively uninspired reprises of “Dancing Queen” and “Super Trouper” et al, there are numerous and rather draggy ballads, e.g., “Andante, Andante” (1980) which I’m almost positive I’ve never heard before and I don’t feel like I’ve been missing out all these years.

“Mamma Mia 2” is equal parts prequel and sequel. The sunny Lily James (“Downton Abbey,” “Baby Driver”) plays the energetic and adventurous young Donna in the 1979 flashback sequences, and she’s joined by a bunch of likable young actors playing the 30-years-ago versions of the Firth, Brosnan, Skarsgard, and the Christine Baranski and Julie Walters characters (Tanya and Rosie, respectively.)

Director/writer Ol Parker executes some neat transition moves as we bounce back and forth in time. The movie pops with bright colors, from the breathtakingly beautiful locale to the costumes to the set designs.

If “Mamma Mia 2” does well, perhaps we’ll get a threequel. I’m picturing Liam Neeson and George Clooney as a pair of long-lost uncles.

Imagine the musical possibilities.

‘Mamma Mia! Here We Go Again’

★★☆☆

Universal Pictures presents a film written and directed by Ol Parker. Rated PG-13 (for some suggestive material). Running time: 113 minutes. Opens Friday at local theaters.