In Stephen Adly Guirgis’ comedy, Our Lady of 121st Street, the dramatic premise is simple enough, even conventional. Basically, it’s another reunion play.

But Our Lady of 121st Street, currently presented by Kitchen Dog Theater, starts off funny, unconventional and raucous — and stays there. Sister Rose, a hard-nosed alcoholic nun who nevertheless made a difference to many Harlem kids, has died, and a number of her former students reunite at her wake at the Ortiz Funeral Home. Except that Sister Rose’s body has been stolen — along with a homeless man’s pants.

Guirgis is a company member of New York’s LABrynth Theater, and it’s clear the playwright often writes to give his fellow actors juicy roles. Which means that Our Lady of 121st Street is somewhat like The Last Days of Judas Iscariot, recently staged by the Risk Theater Initiative. It’s not strong on plot. Or even common sense.

Instead, it’s all about the next crazy loudmouth coming through the door and interacting with all the crazy loudmouths we’ve already met. These include a morose detective with a drinking problem who’s trying to find Sister Rose’s corpse, a grizzled priest who has so little faith left he’s not permitted to say Mass, he’s confined to hearing only confessions, and a brash black drive-time DJ from LA who swaggers back to his old turf only to hide out in the priest’s confessional because he’s terrified of his ex-wife. Drag them all to a nearby bar, throw in a hooker, a mentally damaged young man and a very angry asthmatic, and you can understand why everyone pretty much forgets whatever happened to Sister Rose.

The Christ symbolism is fairly plain here: Sister Rose helps many disreputable sorts, dies and then disappears. And much as in The Last Days of Judas Iscariot, Guirgis is clearly writing about notions of faith and redemption, although he’s doing it in a much more assured albeit more realistic manner.

But after a tremendous series of interlocking comic altercations, the play turns touching — and fizzles a bit. Needless to say, Guirgis hasn’t found a good substitute for the Resurrection.

In all the attention given Guirgis as a hot, new(ish) off-Broadway playwright, he’s often compared to David Mamet — for no reason, really, other than his exceptional talent for highly profane dialogue. That’s about the only similarity. His plays are actually closer to character studies, looking for hope in the midst of contemporary chaos, and as such, they more convincingly recall early Lanford Wilson, before Wilson found the soft, emotional heartland of Talley’s Folly — I’m talking about the gritty, urban Lanford Wilson of Hotl Baltimore and Balm in Gilead.

Directed by Tina Parker, the Kitchen Dog production has terrific energy and life. The show features significant numbers of Southern Methodist University students in the acting and designing departments, and although this means the cast ranges widely in New York accents and in age — it’s hard to believe many of these characters were ever in the same class as kids — it has also meant that Kitchen Dog could field such a sizable cast. And enjoy a nifty little junkyard set. Great soundtrack, too.

But the danger with Our Lady of 121st Street lies with several characters who can slip into being easy comic eccentrics or stereotypes: the philandering black man, the flouncing, insecure gay, the bitter black hooker, the hot-headed Hispanic woman. But Jamal Gibran Sterling and Christina Vela are exceptional as the DJ and his unforgiving ex-wife — larger-than-life, funny yet poignant. Bill Lengfelder brings crusty authority to the priest, and there’s even a small, choice comic turn by SMU student Amelia Johnson as a wallflowerish Connecticut girl, somewhat oblivious to just how out of place she is in this bar.

But it’s Ian Leson, one of the area’s best actors, who is simply superb as the only rational character here, the mentally-damaged boy’s older, caretaker brother. He’s something of the audience’s sympathetic stand-in, and Leson is extremely deft with low-key but sardonic responses to the idiocy and anger around him. When a would-be New York actor eagerly asks him where he could find a $400 apartment, Leson considers for a moment.

“I dunno,” he says — as if stumped by a question on Jeopardy — “Delaware?”