姊妹Jack Linden (Mark Ruffalo) and Hank Evans (Peter Krause) are best friends who both teach at the same university in a small New England town. They both have young children and Jack's wife, Terry (Laura Dern) is close with Hank's wife, Edith (Naomi Watts). But while things appear happy on the surface, there are smouldering pockets of discontent underneath. Financial struggle and domestic boredom has drained the passion from Jack and Terry's marriage, while Hank's numerous infidelities and self-absorption has prompted Edith to find both comfort and sexual fulfilment with Jack. As Jack begins spending more and more time with Edith, it becomes obvious to Terry, whose anger culminates in a sexual encounter with Hank. Now that the deception has come full circle, both couples are left to decide the futures of their shattered unions...