When Ira Black (Chris Messina, “Six Feet Under”) considers joining a gym, he meets Abby Willoughby (Jennifer Westfeldt, Kissing Jessica Stein), the gym’s alleged salesperson, who quickly talks him out of applying for membership. They fall madly in love. They meet and marry on the same day, setting up a slew of complications, such as the meeting between Ira’s upper West Side analyst parents, and Abby’s free spirited freewheeling rentals.

Ira finds out that Abby, not yet 30, is twice divorced. This sends him into a jealous frenzy. He feels his whole marriage is based on a lie, mostly because they don’t know each other.

They get divorced. Meanwhile, Ira’s mother, Arlene (Judith Light, “Who’s the Boss?”), is having an affair with Abby’s father, Michael (the incomparable Fred Willard, For Your Consideration), and three marriages fall into chaos.

There are some genuine funny moments in the script. Screenwriter and lead actor Westfeldt manages to take some tired themes and make them her own.

The film would be a depressing disaster if not for the talent of the cast. The movie rests on the comic abilities of Messina and Westfeldt. Messina exudes a neurotic charm. Westfeldt’s quirky Abby is a joy to watch. Her delivery of her dialogue sparkles, probably because she wrote it.

A series of surprising cameos fill out the rest of the cast, a “Seinfeld” regular and two “Saturday Night Live” alums pop up as therapists, analysts and assorted masters of psychiatry.

Grade: C+

Ira & Abby releases in theaters Sept. 14.