Please come back, Christopher Nolan. Big, historic movies like your upcoming World War II epic “Dunkirk” are important, your ingenious magical mysteries like “The Prestige” and “Inception” are remarkable. Even your misfire, the theoretical-physics science fiction odyssey “Interstellar,” was rich in its sweep and themes.

But you will never be better loved or longer remembered than for your classic Batman trilogy. So please come back and help the DC Comics media franchise. It needs you.

Holy mackerel, does it ever. “Suicide Squad,” the latest effort by Warner Bros. to launch a series of interconnected superhero films, is another example of the bottom falling out of DC’s extended universe.

This is what happens when the comic book fanboys have taken over the asylum. It is damaged goods from the get-go, the kind of film grown in a petri dish in Hollywood. The only way it could have been greenlit into production is through a terrible accounting screw-up.

The quasi-plot concerns U.S. security honchos recruiting a troop of really bad guys to combat even worse ones. It delivers 130 minutes of mind-killing gibberish that could have been scripted by a team of indecisive grade-schoolers.

Writer/director David Ayer shuffles dark antihero concepts from “The Dirty Dozen” and “Deadpool” with a dash of outsiders’ teamwork from “Ghostbusters,” all of which are much better. His film sends a motley crew of small-time villains from DC Comics to smack down an ancient evil force. Never does he reach the Marvel level of on-point humor, compelling characters and general fun. Every cast member with a speaking role plays a person in serious need of mental care, even in the repeated family flashbacks designed to convince us that these killers have hearts of gold. The studio needed a PG-13 crowd-pleaser, after all.

The troops include Deadshot (Will Smith), a top firearms assassin with limited interpersonal skills (“I’m not a hugger”); Harley Quinn (Margot Robbie), a psychiatrist at Arkham Asylum who became the brain-damaged right-hand girl of the lunatic Joker (blink-and-you-miss-him Jared Leto); a boomerang thrower called Captain Boomerang (Jai Courtney); a guy with reptilian skin called Killer Croc (Adewale Akinnuoye-Agbaje); a flame-summoning L.A. gang banger gone pacifist nicknamed El Diablo (Jay Hernandez) and others.

If that’s not overkill enough, we get Katana (Karen Fukuhara), a noncriminal volunteer whose deadly ninja blade absorbs the souls of its victims, a superpower gracelessly plunked into a single scene.There’s also the assigned military leader of the team, Rick Flag (Joel Kinnaman), who can detonate explosive charges in their necks if they disobey orders. His lover is archaeologist June Moone (model-not-quite-turned-actress Cara Delevingne), whose nearly uncontrollable alter ago is Enchantress, a maleficent witch from deep prehistory.

An exhausting list already, and you should see how many more footnote roles and subplot characters are piled on in the movie. They don’t all have expository pet names. (June Moone? Where is the exit?) Viola Davis delivers the film’s only no-nonsense acting as Amanda Waller, a government security official who proposes letting the feral force out of prison. Enchantress, who served as Waller’s secret agent before escaping her control, now wants to exterminate human life. She was once worshiped as a goddess and now wants revenge for being ignored, because enough people didn’t die over the past 6,000 years.

Maybe the film’s overpopulated cast list put her in a killing mood. Absolutely no operative onscreen has an ability that’s essential to the story. Boomerangs? Please. Smith’s Deadshot aims and shoots with all the grace of those air dancer puppets you see in front of third-tier car dealerships. Robbie’s Harley Quinn whacks her opponents with a baseball bat, which does not seem like the kind of thing you crack people out of solitary to do. The skill Robbie mainly contributes as Quinn is putting a pimped-out sway in her hips for repeated fanny shots.

Those moments are more compelling than the boring armies of faceless zombie fodder the team battles, or the generic cauldron of spooky lights blazing from the center of Midway City up to the night sky. Whatever doomsday spell Enchantress is brewing, it takes a long, long time to cook.

I don’t know it for a fact, but I’m convinced it’s a tedium ray aimed at the audience.