On the surface, William Mastrosimone's "Extremities" is about rape and the psychic and physical toll it takes on a woman. But the longer you watch this savage drama (at Source Theatre's Main Stage through Dec. 21), the more you realize that its real subject is something else: the violence lurking in all of us.

This is not theater for the faint of heart. Directed unflinchingly by Dorothy Neumann and acted intensely by a cast of four, "Extremities" is as abrasive as the buzz of a mad wasp. It does not ask to be liked -- many will find it both too graphic and too unsavory for that -- but it cannot be dismissed.

In the opening scene, Marjorie (Jane Beard) is stripped and brutally assaulted by a crazed workman (Steven Dawn) who has forced his way into her apartment. Spraying his eyes with a can of insect repellent, she manages to immobilize him. Then, seizing on his momentary helplessness, she binds him in ropes and chains.

There's a quick blackout, and when the lights come up, he's imprisoned in the fireplace. The tables are now turned; victim becomes victimizer. With cold fury, Marjorie proceeds to torment what she calls "the animal." She jabs him with a poker, douses him with gasoline and then casually flicks burning matches his way. If she has taken justice into her own hands, it's because she is sure she'll have trouble proving her case to the authorities. "Before they'll believe a woman in court," she notes bitterly, "she has to be dead on arrival."

Mastrosimone's play is not subtle, but it is clever in one respect -- the way it toys with our sympathies, shifting them from Marjorie to her attacker and then back again. Marjorie's two roommates (Barbara Klein and Katrina VanDuyn), arriving on the scene, will undergo a similar change of heart. At first they are appalled by what's occurred. Then they see the tortured creature, huddled ignominiously in the fireplace, and they can't help wondering who the real victim is. Mastrosimone has a rude awakening for everyone.

Neumann pitches a few too many moments at excessive decibel levels, and she has a curious tendency to relegate the action to the fringes of the stage. The apartment set, designed by Matthew Cooper, is depressingly ugly, which matters less than the fact that it seems to disobey basic laws of architecture. Otherwise, this is a strong showing by a company not afraid to hurl itself headfirst into some elemental emotions.

Back in the cast after a month's illness, Dawn makes the attacker terrifyingly unpredictable (you're never sure whether the character is truly in pain or just faking it to gain an advantage). Beard vibrates convincingly between uncontrollable hysteria and an implacable desire for revenge. And Klein and VanDuyn provide sharp contrast as the roommates -- the one trying to handle the inflammatory situation reasonably, the other preferring simply to forget it ever happened.

Violence doesn't go away that easily, however. In Mastrosimone's view, it is a quick-spreading plague. More than an antirape tract, this angry drama is antirage.

Extremities, by William Mastrosimone. Directed by Dorothy Neumann; set, Matthew Cooper; lighting, Carol B. Fishman; fight choreography, Lory Leshim. With Steven Dawn, Jane Beard, Barbara Klein, Katrina VanDuyn. At the Source Main Stage through Dec. 21. Source's Midnight Series

Tomorrow night in Source's Warehouse Rep, Theatre Grottesco, a Paris-based company of American actors, will launch what Source is calling its Midnight Series: Friday and Saturday night performances that begin at the witching hour. The inaugural show is an hour-long comedy, "The Insomniacs," about a sleepless husband and wife, whose escalating late-night games all but destroy their house.

Unveiled last week at the French Embassy, "The Insomniacs" unfolds mostly in mime, punctuated by grunts and groans and occasional bursts of gibberish. The actors -- Elizabeth Wiseman and John Flax, wearing nightshirts and bulbous half-masks -- are well grounded in broad physical comedy, acrobatics and commedia dell'arte techniques, but "The Insomniacs" will make you think mostly of the early plays of Eugene Ionesco. Here, as there, simple everyday props proliferate rapidly and transmute themselves into the stuff of surrealistic dreams. The final minutes are conducted in the inflated style of grand opera.

Much of this is original and inventive. Nonetheless, the piece would benefit from trimming and a tighter pace. The pandemonium is slow to gather and you may find yourself thinking at the three-quarter mark that it's time for "The Insomniacs" to go to bed.

Theatre Grottesco will also perform on Saturdays and Sundays at 3 p.m. and Monday and Tuesdays at 8 p.m., at which time "The Insomniacs" will be paired with a one-character work in progress, "The Gryphon." A denser and more intriguing piece, the latter is performed by Paul Herwig, fantastically costumed as the furry mythological beast.

There are threads of story -- apparently, the gryphon was once a young man, who committed a terrible crime; for his sins, Apollo changed him into a monster. But the foul creature is arresting primarily as a living symbol of man's dual nature. Tied to the dank earth, he yearns for infinity; thirsting for beauty, he kills the rare songbird, suspended above him in a cage. Cocteau, I think, would have approved.

The Insomniacs and The Gryphon.Evolved and written by Theatre Grottesco. With Elizabeth Wiseman, John Flax, Paul Herwig. At the Source Warehouse Rep through Dec. 7.