John (John C. Reilly) is "borderline desperate," he says. A more accurate description would be "totally desperate."

Divorced for seven years, the central character of "Cyrus" can't seem to find a woman to replace his ex and still close friend Jamie (Catherine Keener, queen of indies such as "Please Give"), who is about to marry someone else. Then John reluctantly accompanies Jamie and her fiance to a party, where, drunk and rowdy, he amazingly hooks up with Molly (Marisa Tomei) -- beautiful, loving and complete with baggage.

The baggage is her obese 21-year-old son Cyrus (Jonah Hill of "Superbad," "Get Him to the Greek"), who still lives with her. Sure, Cyrus is delighted to meet John and happy to "have a new dad." So he says. But his relationship with Molly is unusual, at the least, and Cyrus starts subtly to sabotage John's relationship with her.

Jay and Mark Duplass ("The Puffy Chair") co-wrote and co-directed this comedy, which, despite an obviously low budget -- or maybe because of it -- is poignant and true to life, starting with John C. Reilly's shlumpy appearance. The dialogue rings true all the time, and the situations avoid melodrama or forced crises.

The tension between John and Cyrus is sharply developed. Where have John's white Adidas sneakers gone after the first time he spends the night at Molly and Cyrus's? We wonder how long it's going to take John to discover that Cyrus is a creep and a liar, despite his apparent candor. Cyrus discusses his mother's sex life with her new lover. That alone is squirm-worthy.

What's oddly unreal is that nobody -- not Molly, not John, not Jamie, whom John consults about the Big Life Questions -- ever even mentions therapy, despite Cyrus's night terrors and anxiety attacks or his peculiar bond with his mother. Hey, it's the 21st century, not the 19th.

Also annoying is some of the cinematography, by Jas Shelton, who likes to make sudden little zooms whenever there's a closeup. We're looking at Marisa Tomei's face, and then we're looking at her a few inches closer up.

But it would take more than that to wreck a charming movie, with performances that are flawlessly true-to-life.