To understand the psychology behind a lie is to clarify something fundamental about the one telling it. By the end of Alan Ball’s All That I Will Ever Be, however, clarity about the liar remains elusive—one of those mysterious riddles inscrutably wrapped in an impenetrable enigma, despite some satisfying psychological penetration on the part of the playwright. The liar is Omar, retail worker in L.A. by day, escort on the Hollywood outskirts by night. He’s Lebanese, Moroccan, Egyptian or French—or he’s Carlito, Puerto Rican papi. You want desperately to care about him, but which “him” do you mean? And Omar had better select a single story soon: Swarthy, lanky and sexy can only get you so far when you’re over 35—the age when a gay escort’s expiration date is plainly approaching in the rearview mirror.

Or Omar (an uneven but affecting Peter Macdissi, of “Six Feet Under” fame) can just keep lying, even as he falls for Dwight (a charismatic Austin Lysy), a young client living off the wealth of his father (Victor Slezak in a small, compelling role) while gorging on sex, weed and self-pity over the long-ago suicide of his mother. When, during sex with Omar, Dwight blurts an orgasmic racial slur (“Fuck me, Osama!”), the seeds of an unlikely connection are forged between them. And naturally it must unravel as Omar’s ever-shifting story finally sabotages him.

It takes a similarly unlikely (maybe even implausible) sequence of events to get Omar to that point. For example: After a bisexual escapade in Act 1, a scene in Act 2 between Omar and Raymond (an older gay man played by an excellent David Margulies) cracks Omar’s brittle outer shell. Whoever he is or was, Omar sees that the soul he enigmatically wrapped inside that mysterious riddle is now like an endangered species. And to play this requires a kind of long-form emotional acting that Macdissi has only begun to fully put together.

Directed with alacrity and insight by Jo Bonney, Ball’s play, if never affirming who Omar is, does provide the other actors with the basis for fine performances. Margulies, as noted, is terrific—one of the most beautifully honest portrayals of an older gay man ever. And Patch Darragh, who plays a small gallery of minor roles, is chameleonic—a cute waiter hitting on Dwight in one scene, the boyfriend of Beth (a talky Kandiss Edmundson) in another.

Other critics have written that All That I Will Ever Be feels like a teleplay, but that’s too facile. No, the problem here is Ball offers a compelling psychological portrait without applying all the colors to the canvas—even if we expect more from the man who wrote the screenplay to American Beauty and created “Six Feet Under.” Another rewrite would have revealed the truth, I suspect, behind Omar’s web of lies. (Leonard Jacobs)

Through March 11. New York Theatre Workshop, 79 E. 4th St. (betw. 2nd & 3rd Aves.), 212-239-6200; $60.