Based on a pair of short stories by Andre Dubus, this drama brings two marriages and four lives to a crossroads by infidelity. Jack (Mark Ruffalo) is a college professor whose marriage to Terry (Laura Dern) has been going through a rough patch. Beyond the tensions over Terry's failings as a mother and housekeeper, Jack is deeply infatuated with Edith (Naomi Watts), the beautiful wife of his best friend, Hank (Peter Krause), a fellow professor and struggling poet. As it happens, Edith is also attracted to Jack, and they soon begin an affair that Edith is certain will soon be found out. Hank, meanwhile, is a man with a flexible attitude about his own fidelity, and he falls into a relationship with Terry. Before long, all four parties learn about the infidelity of their spouses and friends, with differing reactions; Terry becomes desperate to save her marriage, Jack decides he's in love with Edith, but neither couple is willing to divorce.