As played by Jonah Hill ("Get Him to the Greek") in the new dramedy by writer/director siblings Jay and Mark Duplass, the 21-year-old Cyrus lives at home with his single mom, eschews things like "school" and "work," and spends his time composing techno tunes on his cache of synthesizers.

That all adds up to trouble for John (John C. Reilly, "Cirque du Freak: The Vampire's Assistant), a sad-sack loser who's been mired in depression since his wife, Jamie (Catherine Keener, "Percy Jackson & the Olympians: The Lightning Thief"), left him "¦ seven years ago.

Still friends, Jamie drags John to a party, where he strikes out with women, gets drunk, urinates in the bushes and, during that last act, meets the girl of his dreams.

"Nice penis," she says.

Her name is Molly (Marisa Tomei, "The Wrestler") and, for whatever reason " maybe it's the genitals, maybe it's his drunken sing-along to Human League, perhaps it's both " she digs John. They sleep together, but she won't stay the night. Soon, the pattern repeats itself. What's she got to hide?

Paranoid, John tails her home one night. The next morning, he pokes around the property and is greeted by Cyrus. At first, the young man is all buddy-buddy with John, but when it's clear that he and Molly mean business, Cyrus turns into an evil master of mind games.

"Cyrus" falls into the cinematic style known as "mumblecore." More of an anti-style, it's a lo-fi, no-frills indie movement characterized by little funding and lotsa improvising. The Duplass boys helped popularize the genre with "The Puffy Chair" and "Baghead"; the only difference here is using recognizable faces.

And that difference makes all the difference. I find mumblecore to be entirely pretentious, primarily because of its amateurish actors and their "look at me; aren't I arty?" attitude. But professional thesps like Reilly, Tomei, Hill and Keener can deliver lines convincingly, and play both sides of the comedy/drama equation with delicate balance.

One thing I appreciated most about the Duplass' on-the-fly approach is how in-your-face the camera gets; you can see every wrinkle and crinkle on Tomei's face, and it only makes her look lovelier than ever. The brothers don't bother focusing during zooms or the like, so expect no gloss.

Don't expect big laughs, either. Despite marketing efforts to turn Cyrus' dinner-table plea of "Seriously, don't fuck my mom" into a catchphrase, the film isn't about punch lines. There are plenty of funny moments, but they're designed to provoke smiles more than bellyaches. Besides, the story is bittersweet and often dark, or at least in overcast shades of gray. —Rod Lott