''Incidentally, accidentally!'' That's how meaning a heinous offense creeps into a writer's work, according to desperate scribe Katurian K. Katurian (Billy Crudup), whose grim and mostly unpublished short stories are the center of a child-murder case. The investigating officers (Jeff Goldblum and Zeljko Ivanek) represent a police state, and thus tend to eschew literature in favor of the sort of empiricism only electrodes can elicit. But The Pillowman, a gleefully uneven thriller from Martin McDonagh (The Beauty Queen of Leenane), quickly reveals intentions beyond the Kafkaesque. (''I don't usually go in for -esques,'' Katurian haughtily explains.) McDonagh absolves neither the artist nor the art, instead declaring both monstrous while celebrating the comic abomination of it all. It's a metaphysical knot the playwright can't quite untie, even in nearly three hours. But the cast especially Goldblum, disciplining his Morse-code delivery is having a ball.