Brother, Can You Spare My Sanity? Here they are, New York, the ultimate brother-and-sister act, a pair of genetically matched hams who combine the narcissism, fearfulness, shabbiness and splendor of every actor who ever walked the boards. They are also competitive and codependent in a fierce, scary way that is particularly associated with show people and siblings. Just put them on a stage, then step back and watch them burn, possibly to a pile of ashes. Playing the title (and only) characters in "The Two-Character Play," Tennessee Williams's rarely seen fever dream of an eternal folie à deux, Amanda Plummer and Brad Dourif don't just strike sparks. They're a raging conflagration that keeps changing form and direction. "Your variety is too infinite for me," the actor-manager Felice (Mr. Dourif) wearily tells his sister and leading lady, Clare (Ms. Plummer). And he ain't said the half of it. In a sensational return to the New York stage, Ms. Plummer is all quicksilver shifts of theatrical style and emotional substance in this late, demented work from one of America's few genuinely great dramatists. The show opened on Wednesday night at New World Stages, directed with paternal care and indulgence by Gene David Kirk. Ever since she wowed Broadway in a Tony-winning performance as a vision-plagued young nun in "Agnes of God" (1982), this elfin woman has been a changeling performer like no other, seemingly moving to eerie and erratic music that no one else can hear. The last time I saw Ms. Plummer she was unusually subdued, bringing clarity and restraint to an earlier Williams misfit, Miss Alma in "Summer and Smoke," in a 2006 production in Hartford. For Clare, she pulls out the stops, which is exactly what the part requires. Like Alma, Clare is partly a reflection of the man who created her. But in this case, it's a self-portrait of a raging paranoiac, blessed and cursed by a talent he can no longer control. Clare is only half of the portrait provided by Williams in this work, which he described as his "most beautiful" since "A Streetcar Named Desire." The other part of the diptych is Felice, a playwright as well as an actor who sets the stage (in all senses) for the performances (also in all senses) that he and Clare give. Mr. Dourif, in his first stage appearance in decades, has memorably portrayed a variety of lunatics on screen ("One Flew Over the Cuckoo's Nest," "Ragtime," even "Child's Play," in which he is the voice of the killer doll, Chucky). But compared with Ms. Plummer's Clare, his Felice is the sane and centered one, the ego to his sister's id. Or so you think at first. Felice and Clare take turns being taunter and comforter, patient and doctor, obstructer and supporter. They are, after all, of the same flesh and blood and of the same past, which is less palpable but just as powerful. Watching Ms. Plummer and Mr. Dourif, you never doubt that their characters are both kin and kindred spirits. Each is the other's bulwark against a cruel and derisive world, which does not mean that each isn't utterly alone and knows it. "The Two-Character Play" was produced by David Merrick in 1973 on Broadway, where it ran for 12 performances under the title "Out Cry." Though critics were mostly respectful, if baffled, you can understand why it failed. It's low on plot and high on poetry, and it presents the painful spectacle of a talented, desperate mind chasing itself in circles. It probably didn't help that the stars of "Out Cry" were the young and beautiful Michael York and Cara Duff-MacCormick. In his stage directions, Williams writes of Felice, "He has a quality of youth without being young." That's a trait shared by Mr. Dourif and Ms. Plummer here. They evoke the yoked, children-at-play rhythms of a couple who grew up - or rather, never grew up - together. And if you know anything about Williams's life, you will certainly think of his relationship with his sister, Rose, the defining love of his life and by then long confined to a mental institution. The play, and the play within the play, are set on a bleak and dusty stage, occupied by decaying furniture. Alice Walkling is the set designer. It is here that Felice and Clare arrive to discover that the troupe they have been traveling with has abandoned them. Yet an audience and critics (Clare spits at the mention of them) are showing up anyway. This means they will have to do the only appropriate work in their repertory, "The Two-Character Play." It is, you won't be surprised to hear, a Southern Gothic affair, in which a brother and sister named Clare and Felice spend their lives as prisoners in the rotting house where their parents met a bloody and melodramatic end. The script isn't entirely fixed, or can't be entirely remembered, so Clare and Felice are forced to improvise. Making it up as they go presents great opportunities for sibling rivalry, and Mr. Dourif and Ms. Plummer give truly hilarious forms to that power struggle. Watch how they turn an upright piano into a weapon of artistic war. Mr. Kirk, who recently directed a well-received version of this work in London, consistently finds the gallant gallows humor in it as well as the pathos. The reality-and-illusion games à la Pirandello that are played here were old hat even when Williams began working on "The Two-Character Play" in the 1960s. I certainly can't defend it as a cohesive or entirely original work of art. By the end of its much weaker second act, when its symbols overpower its people, it has come to feel like a goulash of avant-garde leftovers. But if acted by the right performers, as it is here, "The Two-Character Play" has a power that cuts deep. Williams, who seems to have been in a state of nervous breakdown much of the time he was writing it, might have been just venting here. But what he's venting is the accumulation of a passionate and obsessive life in the theater, a place that was both his refuge and his torture chamber. Ms. Plummer and Mr. Dourif's Clare and Felice occupy this prison and playground with the mad assurance of people who were born in a trunk and will no doubt die there, too. The Two-Character Play By Tennessee Williams; directed by Gene David Kirk; sets by Alice Walkling; costumes by Lara de Bruijn; sound by Philip Hewitt; lighting by Jake Fine; technical director, Dean Denmon; fight director, Rick Sordelet; associate producer, Ron Johnson Jr.; production stage manager, Lindsey Alexander; general manager, Brierpatch Productions. Presented by Robert Driemeyer, Morgan Sills, Jim A. Landé, Al Parinello and Somerled Charitable Foundation, in association with Robert Barry Fleming, Julio Montalvo, Ted Seifman/Jamie deRoy and Jan Warner. At New World Stages, 340 West 50th Street, Clinton, (212) 239-6200, telecharge.com. WITH: Amanda Plummer (Clare) and Brad Dourif (Felice).