During a torrential rainstorm, David Weinberg, a lawyer in his fifties, and his much younger wife Alexis race to catch the last ferry to their private island. Along the way they spot an injured young man by the roadside and reluctantly give him a ride to the nearest town. After missing the ferry, they check into a motel and plan to catch the next day’s boat; the young man is also on the ferry, though they never meet him directly again during the trip.
David and Alexis have a troubled seven-year marriage, marked by miscommunication and missed chances. In an effort to repair their bond, David arranges a romantic sailing excursion, but a dense fog bank derails their plans and they run aground. They soon discover the young man camping on the shore and, after an initial misunderstanding, invite him to share their fire. David enlists his help to unground the sailboat and invites the traveler into their home.
That night, Alexis dreams she has given the young man a blanket and that her husband has attacked her out of jealousy. In the morning they discover he has cooked them a lovely breakfast, and it becomes clear that David was the one who delivered the blanket to him. David invites the young man to stay for dinner to sample his cooking, then leaves to play golf. Alexis and the man spend time together, drinking whiskey and chatting about themselves, dressing up in the boat house for fun. The man explains that he is a poet, though he cannot write, and shows Alexis his work, all in different handwriting. He persuades her to dictate a dark poem about drowning. They go on a mushroom-hunting walk in the woods, and Alexis warns him away from a mushroom she says would kill him in minutes. She demonstrates how to distinguish it from a nearly identical one that is an aphrodisiac, and after trying to convince him to eat the aphrodisiac, they return home and he apologizes.
David returns from golf, feigning illness but recovering enough to prepare dinner for them both when reminded of the challenge. Their plan to return the man to town is thwarted when David takes him aboard a boat that breaks down halfway, leaving the stranger no option but to stay another night, which he does not seem happy about. The next morning, David provokes an argument with Alexis and briefly fights with the young man, who hides in a shed when David pursues him. When David corners Alexis in the woods, she declares that their relationship is over and later finds the young man on the ground. He seduces her, pressing her to eat one of the mushrooms. Unlike before, she does not resist.
A funeral follows as the young man’s poem, written in Alexis’ handwriting and signed by her, is read as if it were a suicide note. David then returns to the island by boat, strips off, and swims ashore through icy water, as if washing away his former life.
Some time later a hooded stranger arrives at the house, and when the person kisses David, it becomes clear that the young man is the visitor. The two share a kiss, and it becomes abundantly clear that they are lovers and that Alexis’ death was part of a plan between them.
