Quadruple the heroes, quadruple the quality.

Such is the case for “The Avengers,” the first in Marvel’s cinematic canon to be an honest-to-goodness grand slam.

“The Avengers” follows Iron Man (Robert Downey Jr.), Captain America (Chris Evans), the Hulk (Mark Ruffalo), and later Thor (Chris Hemsworth), who are assembled when Thor’s brother Loki (Tom Hiddleston), is brought to Earth through a portal created by the Tesseract, a cube with unlimited energy.

Led by Nick Fury (Samuel L. Jackson) and aided by Hawkeye (Jeremy Renner) and Black Widow (Scarlett Johansson), S.H.I.E.L.D. is charged with stopping Loki before he and the alien Chitauri race go to full-scale war to enslave Earth over the rights to the Tesseract and its power.

Lost in many of the overblown, action-riddled Marvel films is story. Neither the “Iron Man” films, despite Downey Jr.’s charisma, nor the woeful Sam Raimi “Spider-Man” films, for example, were able to keep up much of a cohesive narrative with so many things exploding in the distance.

“The Avengers” is different.

Director Joss Whedon, the pop culture guru whose credits include “Buffy the Vampire Slayer” and “Firefly,” brings a melodious mesh of humor, story and ass-kicking action to the table. “The Avengers” is not offensively stupid like a lot of its superhero ilk, which is a breath of fresh air in a climate of bourgeois cinema favorites adopted from comic books such as “Transformers.” Rather, “The Avengers” is a total blast without ever resorting to too many gratuitous shots of Johansson’s lady lumps and leg-humping dogs.

Perhaps more commendable is Whedon’s symbiosis of different universes. Whedon likely had to walk on egg shells writing a script combining character and story arcs of beloved heroes with devoted individual bases, and the end result is one that’s largely faithful and without too much clunky exposition.

If there’s any semblance of a complaint, it’s that “The Avengers” is a bit slow in parts. At 143 minutes, “The Avengers” isn’t particularly swift, but once S.H.I.E.L.D.’s invisible airship starts blowing up and New York City is later invaded by the gnarly Chitauri warriors, “The Avengers” shifts into overdrive and delivers one of the most awe-inspiring final acts in recent memory.

It also needed more Hulk, who was largely the most enjoyable Avenger to watch, especially near the end, when he provides much of the film’s comic relief.

That’s nit-picking, however, as “The Avengers” is a true romp, one that’s both fun and funny without ever feeling too frivolous. Even Loki, who wasn’t especially menacing in 2011’s “Thor,” was a surprisingly sufficient villain, even if he doesn’t carry the same star power as some other Marvel-universe baddies.

In fact, when Captain America instructs the Hulk to “smash,” he foreshadows “The Avengers’” success, as that’s exactly what this film will be, both critically and financially.

“The Avengers” is rated PG-13 and is slated to hit theaters Friday.

Grade: A-