What a load of fun.

Sometimes in the white-hot center of summer, all we’re looking for is a whiz-bang sci-fi adventure saga featuring a host of familiar and beloved characters (and increasingly familiar faces) having another adventure that falls somewhere in the middle of the spectrum on their overall epic adventure.

Even with its big-screen pyrotechnics and its feature-length running time, “Star Trek Beyond” plays like an extended version of one of the better episodes from the original series, and I mean that in the best possible way.

There’s nearly as much light comedy as gripping drama, nearly as much talk of family unity as end-of-the-world gloom and doom.

It’s a welcome break from all the “heaviosity” in so many recent franchise films, with superheroes bickering over the collateral damage they cause and government agencies debating whether the good guys are really bad guys, and men in capes and costumes nearly paralyzed by their inner existential conflicts.

“Star Trek Beyond” is directed with kinetic enthusiasm by Justin Lin (“Fast and Furious”) and is bolstered by the return of the tight ensemble cast including Chris Pine as Capt. James T. Kirk; Zachary Quinto in that fabulous Ringo wig as Spock; Zoe Saldana as Uhura; Karl Urban (a deadpan delight) as Bones; John Cho as Sulu; Simon Pegg (who co-wrote the script) as Scottie, and the late Anton Yelchin as Chekov.

(The film pays tribute to Yelchin and to the late Leonard Nimoy with subtle class.)

As hardcore Trekkers (Trekaholics? Trekadekafanatics?) know, “Beyond” is the third installment of the alternate timeline reboot that kicked off with the fantastic and simply titled “Star Trek” in 2009 and continued with the smashing “Star Trek Into Darkness” in 2013.

“Beyond” picks up some 966 days into the five-year mission of the U.S.S. Enterprise. (Geek alert! The original series debuted on NBC in September of 1966: 9/66.)

Kirk and Spock are questioning their commitment to the mission, for very different reasons.

In fact the whole crew is in something of a rut. Another day, another encounter with an alien life form, another threat to the ship and crew, another victory, another lesson learned about the importance of disparate cultures learning to get along. To what end?

Kirk applies for a supervisory position that will ground him. Spock and Uhura are “on a break.” Spock is driving Bones crazy. Sulu and Chekov are stuck in background shots, waiting to deliver what precious few lines they have. Scottie’s crabby.

Maybe this collective funk contributes to the crew of the Enterprise falling for an obvious trap in which a rescue mission leaves them vulnerable and under siege.

Forced to abandon ship, trapped on a hostile planet teeming with aliens that want to kill them and separated into pairs or alone, the crew of the Enterprise has to set aside internal differences and figure out a way to band together to save themselves and of course save the universe, because what’s a sci-fi adventure without a megalomaniacal villain who wants to blow up all of creation so he can rule what’s left of the rubble?

In this case the alien villain is Krall, played by the great Idris Elba, nearly unrecognizable beneath his fantastically cheesy Krall mask and makeup. (It feels as if many of the alien beings in “Beyond” are outfitted with deliberately retro rubber masks and old-school costumes, which is going to make it easy for Trekkers to duplicate the look for all the Comic-Cons and other Cons to come.)

Krall’s suitably nuts and Elba has a powerful dramatic scene late in the film when we learn his true motives — but the real breakout star on that alien planet is Jaylah (Sofia Boutella), who moves like a jungle cat and looks a little like a model in an edgy ad touting Fashion Week. Jaylah is a fierce warrior and she’s hot, and she’s loyal and a little weird, and there’s just the slightest chance she might be attracted to the nerdy Scottie.

In other words, she’s pretty much every fanboy’s fantasy woman.

At times “Star Trek Beyond” gets a overcrowded, what with the twin crises Spock and Kirk are grappling with; the apparent death of one character who’s still alive; the game of hot potato with the MacGuffin of a device everyone so desperately needs; quick-cut battle sequences where it’s a bit hard to tell who’s shooting whom, and a passing reference to Sulu’s sexuality that happens so fast we barely have time to absorb (and applaud) it.

But once the action subsides and we have a chance to take it all in and reflect on what transpired, it all pretty much makes sense.

In a parallel timeline kind of way.

★★★

Paramount Pictures presents a film directed by Justin Lin and written by Simon Pegg and Doug Jung. Running time: 122 minutes. Rated PG-13 (for sequences of sci-fi action and violence). Opens Friday at local theaters.