“American Hustle” opens Friday at Point, Eastgate, Star Cinema and Sundance. R, 2:17, three and a half stars out of four.

“From the feet up” is a phrase that comes up again and again in “American Hustle.” It’s an expression con artists in the film use to signify full commitment to the role they’re playing.

For his follow-up to last year’s “Silver Linings Playbook,” writer-director David O. Russell has assembled a cast that all perform from the feet up. The result is an entertainingly shaggy riff on the caper film that emphasizes loose, naturalistic performances and comedy over plot and thrills. If you’re looking for a clockwork-perfect crime plot, you won’t find it here. But if you want to hang with some wildly unpredictable and complex characters and wonder who will come up on top, “Hustle” is a lot of fun.

“Some of this really happened,” the opening title card reads, cluing us in to just how much fealty Russell and screenwriter Eric Singer are going to pay to the actual events of the late ’70s Abscam scandal, in which FBI agents posed as Arab sheiks to bribe congressman.

In “Hustle,” we follow the exploits of part-time dry-cleaning magnate/full-time con artist Irving Rosenfeld (Christian Bale). With a majestic pot belly and a combover that’s a triumph of modern follicle architecture, Irving is the most un-Bale like role Christian Bale has taken since “The Machinist,” and Bale seems to revel in getting lost in Irving’s strange mix of predatory scam artists and noble romantic. When Irving falls for Sydney Prosser (Amy Adams), a fellow con artist who passes as a British sophisticate, their merger is both poignant and lucrative.

The bubble bursts when hotshot FBI agent Richie DeMaso (Bradley Cooper) nabs Irving and Sydney in a sting operation. Richie, as tightly wound as the perm curls on his head, makes them an offer; if he’ll use their confidence game skills to help him catch some even bigger fish, he’ll let them go. The couple reluctantly agrees, but as the operation grows bigger and bigger, drawing in not only New Jersey mayor Carmine Polito (Jeremy Renner) and other Garden State politicians but also the Florida mob, Irving and Sydney realize they’re in way over their heads, and start hunting for a way out.

Oh, and there’s yet another wild card in the mix — did I mention Irving is married? His wife Rosalyn (Jennifer Lawrence) is a woozy loose cannon whose loose lips could topple the entire operation.

If that plot sounds complicated, it’s really just the backbeat thrumming behind the performances, as we watch the characters collide with each other, making alliances and then turning on each other. We learn pretty quickly that everyone in the film is a con artist, and the most dangerous ones are the ones conning themselves. Richie believes so deeply that he’s a super-agent that he misses all the warning signs in the operation — as in “Playbook,” Russell uses Cooper’s outsized confidence to suggest delusion. At the other end is Rosalyn, who Lawrence gives a live-wire pathos, unwilling to see how much damage she’s causing to everyone around her. (Lawrence’s bravura scene is singing “Live and Let Die” crazily while cleaning the living room, lost in her own desperate narrative.) Even Renner’s Polito suffers from delusion, so invested in his man-of-the-people image that he’s willing to skate over legal niceties.

Caught in the middle are Irving and Sidney, the two con artists who are paradoxically the most self-aware people in the film. Irving turns out to have a soft heart and a sense of responsibility towards the people he’s pulled into this mess. Meanwhile, Adams finds new dark and needy depths as Sydney, who yearns to be “real” after a life of self-deception, even if she can no longer quite remember (or face) what her “real” self was.

Russell keeps the camera moving and bobbing between all these characters, creating a giddy momentum that keeps pushing the film forward. The film’s Jimmy Carter-era milieu is a lot of fun, from the outrageous plunging necklines on the dresses to the what-were-they-thinking haircuts on the men.

But underneath the seedy glitz, every character in “American Hustle” seems like a real person, and Russell treats them all with empathy and curiosity. He gives these suckers an even break.