Diablo (Jay Hernandez), Boomerang (Jai Courtney), Killer Croc (Adewale Akinnuoye-Agbaje), Harley Quinn (Margot Robbie), Deadshot (Will Smith), Rick Flag (Joel Kinnaman) and Katana (Karen Fukuhara) in “Suicide Squad.” (Clay Enos/DC Comics /Warner Bros. Pictures)

“Suicide Squad” opens not with a bang — or even a whimper — but with a three-ring binder. Wielded by Viola Davis in the role of unscrupulous government operative Amanda Waller, the book in question contains the dossiers and criminal records of members of the titular extra-military fighting unit that Waller is assembling: a hand-picked group of eight mostly incorrigible criminals and a metahuman or two (think the mutants of “X-Men”) to handle the government’s dirtiest, most under-the-rug battles. To ensure their cooperation and loyalty to team leader Col. Rick Flag (Joel Kinnaman), they have been injected in their necks with “nanite” bombs, micro-explosives rigged to go off if they attempt to flee, fail to protect or otherwise disobey their commanding officer.

With me so far?

What takes a few sentences to summarize in print becomes a mostly thankless chore for the audience to decipher in writer-director David Ayer’s carelessly plotted, murky-looking, sloppily choreographed and largely fun-free interpretation of the DC Comics antihero-adventure saga. How, you might ask, is it possible to so thoroughly suck the joy out of a story that features a guy who can shoot flames out of his hands (Jay Hernandez, as Diablo) and a reptilian, sewer-dwelling thug nicknamed Killer Croc (Adewale Akinnuoye-Agbaje, under 10 pounds more prosthetics than Idris Elba had to wear in “Star Trek Beyond”)? It is a mystery almost as deep as the question of why Ayer thought it was a good idea to cast model-turned-actress Cara Delevingne as the film’s villain. Playing Enchantress, a resuscitated witch from the past who inhabits the body of a scientist laughably named June Moone, and who threatens the End of Life as We Know It, the “Paper Towns” actress can at least be counted on to deliver several of the film’s few-and-far-between laughs.

None of them, in her case, are intentional.

Did I say villain? Make that villains. In addition to the witch, there is also her brother: a “non-human entity” named Incubus (Robin Atkin Downes) — although he is never referred to by that moniker — who threatens the world with an army of human minions who have developed the worst case of blackheads you have ever seen.

Jared Leto as the Joker steals every scene he’s in. (Warner Bros. Pictures/DC Comics /Warner Bros. Pictures)

Margot Robbie as Harley Quinn is one of the bright spots. (Warner Bros. Pictures/DC Comics /Warner Bros. Pictures)

And let’s not forget the Joker. As the Clown Prince of Crime, who is intent on rescuing his girlfriend Harley Quinn from Col. Flag’s Task Force X, Jared Leto steals every frame of the film he appears in. Along with Margot Robbie’s delightfully over-the-top shrink-turned-psycho Harley, Leto is one of the film’s rare, pure pleasures. The scene in which the two deranged lovers embrace in a vat of acid — shot from above, and with a swirl of Harley’s blue and red hair dye dissolving into the mayonnaise-like goo — is the most arresting visual in a film that otherwise looks like it was shot through a muddy Instagram filter. A movie about these two, you might gladly watch.

Will Smith officially heads the cast as super-sniper Deadshot, but his character is pretty much dead on arrival. An assassin who turns out to have a heart of gold, unsubtly evinced by his soft spot for his daughter (Shailyn Pierre-Dixon), Deadshot is meant to embody the film’s lite antiheroics: He’s the cynic who dubs the task force “Suicide Squad.” But the character feels mopily obligatory, even when he’s shown single-handedly gunning down a dozen of Incubus’s pimple-people from the roof of a car. It’s one of the few moments in the film designed to elicit applause from the fanboys and fangirls who have been waiting, with mounting anticipation, for the film. But it stands out only because there is otherwise so little badassery in “Suicide Squad.”

A second opinion on “Suicide Squad”: David Betancourt and Michael Cavna of the Comic Riffs blog think the studio has a hit in their hands with their anti-hero team-up epic. (Erin Patrick O'Connor/The Washington Post)

The necessity of sticking to a PG-13 rating may have hamstrung Ayer (“Fury,” “End of Watch”), who had never shied away from darkness and violence. Sadly, “Suicide Squad” feels like a watered-down version of what could have been a stiff drink.

Other than Hernandez’s Diablo, a former gangbanger who is tortured by his violent past, and Karen Fukuhara’s elegantly lethal, ninja-like Katana, there are few among the rest of the needlessly large cast who are memorable. One member of the squad is taken out of action early on, before we even get a chance to see the scope of that character’s abilities. And Jai Courtney, as the Australian Captain Boomerang, barely registers, in a performance that feels like off-brand Tom Hardy. (Hat tip to my 16-year-old son, who came up with that shade.)

That’s the real problem with “Suicide Squad.” In aiming for — but falling short of appealing to — the teenage demographic, the film is a double cop-out, disappointing both fans of the source material’s grown-up gloom-and-doom aesthetic and discerning adolescents. Deadshot may never miss, but “Suicide Squad” does, with almost every bullet.

PG-13. At area theaters. Contains sequences of violence and action throughout, disturbing behavior, sexually suggestive material and coarse language. 123 minutes.