Sam Shepard's "True West" is an ominous tale of sibling rivalry, terrifying and inconclusive. The current Source Theatre production is vehement and often compelling, but as the play becomes more violent it veers out of control.

Control is one of the numerous psychological whips thrashed around in this play. Austin, a slight, intellectual writer, is house-sitting for his mother when his big, brutish slob of an older brother Lee appears unexpectedly. Austin is a college graduate, a family man with a good job, while Lee is an overweight petty criminal and bully. Lee intimidates his brother, and the two rage at each other with the fierce white hatred that even an otherwise reasonable person can feel for a sibling.

"What kind of people kills each other the most?" Lee says at one point. "... family people."

But what might have turned into a Cain and Abel parable is abruptly reversed when Lee outwits Austin at his own profession -- screenwriting, implausibly convincing (or perhaps blackmailing -- it's never clear) his brother's producer to option a story. Austin becomes noticeably unhinged at this point. The role reversal reveals that neither brother has a very firm hold on sanity.

Christopher Henley as Austin and Brian Hemmingsen as Lee are well cast as the brothers. Hemmingsen, particularly, has an air of menace that is all too convincing. Unfortunately, he's also the one who lets his performance run away with him as he not only chews the scenery, but destroys it. Self-indulgence creeps into both performances and they disintegrate into a bewildering furor of fighting, throwing, yelling and setting things on fire. Director Prudence Barry seems to have lost her grip on the second half of the play.

The supporting performers -- Gayle Wilson as the movie producer and Mary Stetina as the mother -- seem unsure of their roles, and the focus of the play shifts when either of them is onstage. Stetina's role certainly is not easy -- who else but Shepard would write a mother who, when she sees one of her sons trying to kill the other, announces she's had enough and is going to check into a motel?

The play, two acts in nine scenes, is preceded by a fortunately brief Shepard work called "Killer's Head." It is an utterly pointless monologue delivered by a man blindfolded and strapped in an electric chair, performed without distinction by Russell Miraglia.

"Killer's Head," by Sam Shepard. Directed by Brian Hemmingsen and Christopher Henley, designed by Bill Holling-sworth, Eric Annis and Gary Floyd. With Russell Miraglia.

"True West," by Sam Shepard, directed and designed by Prudence Barry. With Christopher Henley, Brian Hemmingsen, Gayle Wilson and Mary Stetina.

At the Source Theatre through March 19.