There are some families -- a lot, if you're honest -- you wouldn't want to be part of or even know, but you wouldn't mind visiting, from a safe distance, with your timely escape assured. Such are the losers in Tracy Letts' very dark comedy, "Killer Joe," a guilty pleasure from barebones productions -- which is redundant, that being the company's signature taste.

But this isn't just a gritty comedy about murder, mayhem and sexual predation by a very hot American playwright, most recently author of "Superior Donuts" and "August: Osage County," because barebones has added a dimension outside the script. Pittsburgh rock patriarch Joe Grushecky is present (live at most performances, recorded at a few) to play inter-scene musical commentary, something like a Greek chorus or the old man in a Sam Shepard play. His bluesy rock laments add classy counterpoint, an emotional gravitas beyond Letts' script.

The family is composed of befuddled patriarch Ansel (not yet 40), his curvaceous, demanding wife, Sharla, and his two children from a previous marriage, hapless Chris, 22, and lovely Dotty, 20. They pretty well define trailer trash, a condescending, non-PC term, except they do live in what seems to be an expanded trailer, much like the one in the playwright's similar "Bug" (barebones, 2007) -- and trash is as trash does.

After all, the men grab cans of beer and turn on the TV every time they enter. Trailer trash they are, which doesn't mean they aren't sympathetic, at least in spurts.

Loser Chris is in debt to some bad guys who don't play around, so he talks the family into hiring a rogue cop who arranges killings on the side, to bump off the drugged horror (so they say; we never meet her) who is his and Dotty's mother, Ansel's first wife. The payoff is her $50,000 life insurance policy, payable to Dotty, which the four would share -- after paying off the killer.

Ay, there's the rub.

First, the insurance isn't what they think. Take double indemnity, the true beneficiary, some hidden partnerships and the demands of the killer, then add a quintet of cross-purposes to fuel lickety-split twists to the plot. Soon the slacker tension of the trailer erupts in splendidly sickening, sexually charged violence, choreographed by the Pittsburgh master, Randy Kovitz. Don't bring the kids.

And there's Dotty, a pearl among swine. Sweet and innocently voluptuous, but mentally damaged in childhood, she becomes a form of payment, until it turns out she also has a will of her own. Hayley Nielsen's Dotty is a brave, well-measured performance. Vocally, she's sometimes faint when she turns upstage, but she is inevitably a focus of our concern as we stare at this awful family with disapproving glee from the safety of our seats.

Even Joe seduces us into moments of sympathy -- villains can be victims, too, perhaps even a cold-blooded sexual predator and (obviously) killer. Perhaps it's just that he's played by Patrick Jordan, whom we can't help liking a bit. At least he turns off the TV when he wants to talk business. Jordan's twinkle is here suppressed -- he's never been more steely quiet to good effect.

John Steffenauer plays weedy Chris with the needed self-deceit. John Gresh has never been better than as lumpy, befuddled Ansel, with distant memories of manly instinct barely showing through his self-protective fog. Lissa Brennan's Sharla is perfect, smarter than she seems but nowhere as smart as she thinks. She deserves a kickback from the costume designer, because her tattoos are right at home, and sometimes they're about all the costume she's wearing.

Yes, there's nudity, full and frontal, male and female. But you're already not bringing the kids, because of the sexual violence, remember?

Director Kim Martin keeps the action moving but also gives the characters time to breathe, a compelling rhythm. I'd expect that to be compromised by the musical interludes, but they add so much, it isn't. The play still comes in under two hours.

The backstage artists have done their jobs well. Angela Vesco's costumes neatly melt into set designer Douglas McDermott's atmosphere. Special kudos to whoever is left to clean up afterwards.

Sound (Dave Bjornson), lights (the ubiquitous Scott Nelson) and effects (Benzy) merge to create the compelling sense of rain and distant, haunting thunder. It's invariably scary, but it remains threatening, never bringing a cleansing downpour. The air never clears

The play's like that, too. Titillating and disgusting at the same time, it leaves us to feel complicit in our mix of pleasure and moral distaste. "Killer Joe" is a cold play, in the post-Shepard, post-Mamet Chicago school. It could go any way in Act 2, and it does. We never know the characters well enough to see the necessity in what happens.

This randomness could be a further condemnation of this world. To me, it feels as though the play couldn't find an ending, just further complication. It's more concerned with effect than soul. But when Mr. Grushecky plays a smoky "Save the Last Dance for Me," this "Killer Joe" strums very deep emotional chords.

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