In her third marriage to writer Jake Armitage (Peter Finch), Jo (Anne Bancroft) wrangles her brood of five young children with Jake's cheerful support. But Jo's happiness is shattered when she realizes that Jake is not only unfaithful, but that he is constitutionally incapable of monogamy. Pregnant with another child, Jo becomes increasingly distraught, and eventually breaks down utterly when confronted with more evidence of Jake's infidelity.

The screenplay by Harold Pinter takes a cold psychological look at the interior turmoil of a middle class wife and mother, and begs the question: what is the ultimate cause of Jo's unhappiness? Is it Jake's unfaithfulness? A lack of fulfillment in her maternal role? A fear of losing her role as her youngest children grow?

Director Jack Clayton shines a harsh light on fidelity and marital responsibility in the modern world in this disturbing but sharply crafted drama.