In New York City, there are millions of couples, some young, some old, some happy, and others on the verge of breaking up. In between are those having problems, such as Tom (DAVID DUCHOVNY) and Rebecca (JULIANNE MOORE). She's a famous actress rehearsing for a Broadway show, while he's a stay-at-home dad to their young child.
While they'd seem to have it all, their lack of sexual compatibility has their marriage in disarray, resulting in him taking a liking to single mom Pamela (DAGMARA DOMINCZYK), while Rebecca must contend with young theater worker Jasper (JUSTIN BARTHA) putting the moves on her.
At the same time, her unemployed brother Tobey (BILLY CRUDUP) can't go the extra step with his longtime girlfriend Elaine (MAGGIE GYLLENHAAL), an office worker and aspiring writer. She feels her biological clock ticking, but his obsession with death has left him phobic of marriage.
When she eventually dumps him, he takes up with a married acquaintance, Faith (EVA MENDES), but can't stop thinking about Elaine. As the weeks wear on, the two couples try to sort through their various relationship-based issues.