Usually, it’s a bad thing when a performer sleepwalks her way through a show.

Not when the actress is Rhea Seehorn; not when the play is Marat/Sade. Actually, the play is The Persecution and Assassination of Jean-Paul Marat as Performed by the Inmates of the Asylum of Charenton Under the Direction of the Marquis de Sade, Peter Weiss’ twisty, multilayered assault on audience sensibilities, a fetid and fascinating artifact that, in Peter Brook’s fabled London staging of 1964, apparently had half the patrons cheering while the other half ran shrieking from the theater. It’s still unsettling, even if director Jess Berger doesn’t push boundaries hard enough in Washington Shakespeare Company’s production to get too far under anybody’s skin.

Seehorn plays Charlotte Corday, the exquisite convent girl who murdered the revolutionary thinker Marat in his bath. Or rather, she plays a blank-eyed, white-faced catatonic trying feebly to play Corday—the conceit here, after all, is that the play is fresh from the pen of the Charenton asylum’s most famous inmate, de Sade, and that that worthy, for reasons of his own, has hand-picked his cast from among his fellow patients.

Marat (Christopher Henley) is a paranoiac with a pronounced tic; the role of Duperret, Corday’s chaste, cerebral swain, is quite naturally given to the asylum’s resident sex fiend (an amiably priapic Andy Rapoport). Various degenerates and defectives, alternately pitiful and revolting, play Marat’s devoted companion, a herald, and a quartet of harlequins who comment musically on the action. The exercise is meant to be therapeutic, to prove to the invited audience—to us, standing in for the demimondaines of Napoleon’s Paris—that Charenton’s unusually “humane” methods are working. But de Sade’s agenda, it becomes clear, is a different one.

Seehorn has previously proved her gifts as a comic actress, and in Woolly Mammoth’s Brimstone and Treacle not long ago she established that she could play a mental patient without either stealing focus with mannerism or disappearing into the scenery. But this portrayal is another thing entirely, an intricate and wrenching picture of a terrified, fragile, and even frightening creature, at once reluctant and all too anxious to do the violence that is her charge. If the scenes that play out in Lou Stancari’s dank cistern of a madhouse set are dark and hallucinatory, Seehorn’s performance asks what double horrors must plague this girl as she slips from that milieu into her own private nightmares and back again. Brian Hemmingsen’s de Sade is a brooding, seething, magnetically perverse invention, sitting like a malevolent spider in the wings, and Henley’s twitchy Marat is a pathetic picture of noble aspirations confused, but Seehorn’s riveting performance—her command of the rough poetry in Charlotte’s lines—inevitably draws the focus back to her.

The rest of WSC’s production is nearly as exciting, though occasionally what ought to be a consistently unnerving air of barely suppressed anarchy goes over the top to become camp. And the staging doesn’t do anything to clarify Weiss’ ideology, though perhaps that’s asking too much of any director. De Sade clearly despises Marat: Stepping into his drama’s action to argue with his chief character, he belittles Marat’s philosophies and decries his revolution as working oppressively against de Sade’s ideals of individuality. But Weiss gives the increasingly confused and frustrated Marat time for an impassioned rebuttal in a sudden moment of clarity before his death, and though it’s de Sade who inevitably triumphs, we’re clearly meant to feel queasy about his victory.

It’s not that there needs to be a hero to champion in this sordid spectacle—as if there could be—but it would help if we knew exactly what ideas Weiss wants to argue with us about. Totalitarianism? Revolutionary fervor? Rampant consumerism? Which does he despise most? The playwright never answers the question; moreover, he never leaves us the clues we need to answer it ourselves. Whether it’s an intellectual’s precious detachment, a lack of conviction, or just lazy writing, it’s frustrating—and it means that Marat/Sade, although it’s a rich mine for actors to plunder, isn’t entirely satisfying.CP