Irish playwright Enda Walsh is getting to be a regular in New York. In the past four years, St. Ann’s Warehouse has presented The Walworth Farce, New Electric Ballroom, and Penelope, and now hosts his latest: Misterman, a riveting, if decidedly dark portrait of one man’s disintegration (through December 22, tickets $45-$77).

Recognizable to US audiences as Dr. Jonathan Crane/The Scarecrow from Batman Begins and The Dark Knight, Cillian Murphy makes his stateside stage debut with a knock-your-socks-off performance as Thomas Magill, a pious young man in the small (fictional) town of Innisfree. The cartoonish beginning, as Magill dashes the length of the cavernous performance space in vain attempt to stop a tape player from blasting music, seems a surprising opening for the relatively sober play that follows. But it hints at the unruly nature of the voices Magill hears, and his capacity for violence.

Memory and repetition are prominent themes in Walsh’s plays, and here they manifest themselves in Magill’s obsessive need to replay—literally, via reel-to-reel tapes—the events and conversations of one fateful day. Constantly wearing a portable recording device, Magill restages and repeats his interactions with his neighbors, taking both roles in each conversation. Magill is insufferably judgmental, with more than a touch of missionary zeal, and ends each encounter by scribbling a damning sin about his neighbor in his notebook.

Flipping between Magill and these different characters, Murphy is extraordinary, and sustains a manic energy that is essential in propelling this one-man show forward. It’s often funny, except Magill becomes an increasingly unreliable narrator; his scenes with his “Mammy,” who is represented by a reel player at the head of a table, really ratchet up the demented factor. Without giving away too much, let’s say the ending isn’t surprising, and if anything, its very predictability fulfills the premise that repetition is inevitable.

[For those in the market for Walsh Lite: he has written the book for the musical Once, now playing at New York Theater Workshop and moving to Broadway in 2012.]