Take away the bumbling, gun-happy witness protection security officer (Tom Arnold), the gay cop (Jess Rowland) trying to meet a man on the lonesome highway with his trusty hook-up detection app, the dreadlocked ex-convict (Bradley Cooper) and in-cahoots girlfriend (Joy Bryant) out for vengeance against the man who put him away, and the irritating ex-boyfriend (Michael Rosenbaum) who refuses to accept that his one-time girl is moving away, and what you have left is an irresistible romantic comedy between two people who light up the screen as if they don't even need to act. In fact, they don't, since Dax Shepard (2010's "When in Rome") and Kristen Bell (2010's "You Again") are a real-life couple with chemistry coming out their every orifice. Too gross? Maybe, but it's the kind of joke that would be right up the alley of the overstuffed ensemble of characters in "Hit & Run," a curious genre hybrid also written and directed by Shepard (David Palmer co-directs). High-speed pursuits and shoot-outs mingle alongside long-held secrets revealed, madcap slapstick, and lovelorn pathos. Most of it is good as an amusing aside, but it is the genuine central relationship that turns this off-the-wall free-for-all into more than just a throwaway romp.

Charlie Bronson (Dax Shepard) and Annie (Kristen Bell) have been a happy couple for the better part of a year, living in the quiet town of Milton Valley, CA, and making the best of Charlie's place in the witness protection program. When Annie is offered a dream job at USC, heading up her own teaching department in conflict resolution, Charlie isn't about to let her miss out on the opportunity. Putting his own life on the line to be with her, he agrees to accompany her to Los Angeles. The path to their destination, however, is lined with one pitfall after the next, not the least of them being Annie's ex-beau Gil, who is on to Charlie's dark past. Years ago, it seems, Charlie (real name: Yul Perkins) was the getaway driver in a series of armed robberies pulled off by Alex Dimitri. In exchange for jail time, he agreed to testify against him, and Alex wants payback.

How big of a deal should it be if you were to learn unsavory information about your significant other's past—experiences that are long gone and done with, but that still, nevertheless, are a part of your boyfriend's or girlfriend's history? "Hit & Run" poses this question and can only answer for the couple at the center. Annie has been well aware all along that Charlie has been in witness protection, but what he has failed to mention to her is the real criminal reason why. It's a blow to her when she finds out, forcing her to reexamine how well she knows this kind and generous man she thought she loved. If he could withhold something like that, can she trust him at all? Credit must go to writer-director-actor Dax Shepard and Kristen Bell for how convincingly they are able to develop an onscreen relationship that is not only authentic, but truly candid, beginning with an opening scene in bed so private, adorable and intimate the viewer almost doesn't feel right eavesdropping on their conversation. When these two dynamite performers are together, the film lifts off to a different level, the short-hand details that make up their interactions an immeasurable asset to revealing who they are as people and as a couple. There is a terrific scene where Annie is disgusted when she hears Charlie passingly use the word "fag," chastising him over its age-old connotations and the pointlessness of saying it at all (she does have a doctorate in conflict resolution, after all). It's very smartly written without becoming preachy.

If Shepard and Bell are the glue holding together the enterprise, their co-stars are more of the take-'em-or-leave-'em variety. All of the supporting players could have been cut, turning this into a virtual two-person show, and it wouldn't have harmed a thing. Still, Tom Arnold (2007's "The Final Season") exhibits solid comic timing as Randy, Charlie's clumsy witness protection marshal, and Kristin Chenoweth (2008's "Four Christmases") steals her couple scenes as a profane, straight-shooting college dean. Bradley Cooper (2011's "The Hangover Part II") is always reliable at playing smarmy, and here he's utterly despicable as main villain Alex Dimitri. In one scene, Alex terrorizes a black man for buying cheap dog food at the market by strapping a leash around his neck and dragging him down the sidewalk; it's as ugly as it sounds, and not even giving Alex an African-American girlfriend can make the slave imagery palatable. The rest of the performers aren't worth mentioning—they're neither outstanding or terrible—because, frankly, they're not very interesting and get in the way of what's good about the movie.

"Hit & Run" has a few big laughs—a set-piece involving a car chase pissing contest, with all the automobiles cascading in circles to the song "Pure Imagination," is so ludicrous it works like gangbusters—and a fair share of low points (Alex's discussion of his prison experience goes on too long and is the opposite of funny). When the violence and lunacy subsides, though, what is left is an immensely winning love story about people who realize that despite what may have happened in the past, yeah, they do know each other, and they like what they see. Some audiences will no doubt accuse "Hit & Run" of indulging in excess, but that's okay since the focus almost always remains on Charlie and Annie. They deserve a happily-ever-after ending, preferably scored to Pete Townshend's "Let My Love Over the Door," and that's exactly what they get.