Jazz pianist Tom Stewart (Carlson), who lives on a Cape Cod island community, is preparing to marry his fiancee Meg. Shortly before the wedding, Tom’s old girlfriend Vi (Juli Reding) visits and informs him that she will end Tom’s relationship with Meg, using blackmail if necessary. While arguing on top of a lighthouse, the railing Vi is leaning against gives way. She manages to briefly hang on, but Tom refuses to help and watches her fall to her death.
The next day, Tom sees Vi’s body floating in the water. He retrieves her only to see the body turn into seaweed. Tom tries to forget what he’s seen, but over the next several days, all manner of strange occurrences happen. Vi’s watch washes up on the beach and mysterious footprints appear in the sand. Before long, Vi’s ghost appears and tells Tom that she will haunt him for the rest of his life.
One day, Meg’s little sister Sandy shows up and asks Tom if she can see the engagement ring. As Tom shows it to Sandy, he’s spooked by a disembodied hand that soon makes off with the ring.
Soon afterward, a party is held for Tom and Meg. Vi’s disembodied head makes a small appearance in a photo taken of Tom and Meg, and when he’s alone, Vi taunts Tom that she’ll now use her voice to tell the world how Tom Stewart killed her.
To add to Tom’s dilemma, a ferry-driving beatnik comes looking for Tom, intent on collecting the $5 Vi owes him for her trip to the island. Tom’s haste to pay the fellow off causes the shifty man to stick around, where his attempts to blackmail Tom lead to the ferryman’s death. However, unbeknownst to Tom, Sandy has inadvertently witnessed the murder.
At the wedding, Sandy keeps quiet about what she’s seen, but almost says something at the point in the ceremony where the clergy asks if anyone “can give reason why these two should not be joined in matrimony.” Before she can speak, the church’s front doors burst open and the flowers all begin to wilt as the candles die out, bringing the ceremony to an abrupt and unpleasant end.
Later that night, Tom goes to the lighthouse, telling Vi that he’s leaving the island. Soon after, Sandy listens in to what Tom says. When Tom finds her, he realizes that he’s now trapped; Sandy knows too much and could possibly tell Meg and the others. A desperate Tom leads Sandy up to the broken lighthouse railing with the intent to push her over. But just then, Vi’s ghost swoops down on Tom, causing him to go over the edge as Sandy watches.
Soon afterward, the islanders go searching for Tom’s body. However, the first one they find is Vi’s. Shortly afterward, Tom’s body is found and placed next to Vi’s body, which somehow manages to turn and lay its arm across his body. On Vi’s dead hand is the engagement ring that was supposed to be Meg’s, signaling that Tom is now stuck forever with Vi.