When Ben Ferris finds himself powerfully attracted to Iris Elliot, he warns himself to be careful. Happily married, he has no desire to pursue the beautiful Iris and damage his relationship with his wife, Alice. But when Alice and Iris strike up a strong friendship, one that excludes Ben and the group of friends with whom they are sharing their Cape Cod vacation, he finds his desire for Iris growing along with envy of the relationship the two women enjoy. Alice and Iris spend more and more time together exploring the Cape, and Ben, for his part, starts to fear that their friendship is sexual. As the summer progresses, his desire for Iris and his resentment of his wife continue to grow and when he as much as accuses Alice of sexual infidelity, he brings down upon himself the very damage he at first sought to avoid.