Patricia Bursel stars as Kathrine, who is recovering from a nervous breakdown. Her nurse, Luisa (Sanchez), becomes her caretaker, moving Kathrine to her uncle's estate by the ocean. The two women develop a friendship, but there are some things about Luisa that Kathrine doesn't know, like Luisa's need for sex and pain. Luisa's husband Sonny (Schulze) shows up and insinuates himself into the insular life that Kathrine and Luisa have built, and we discover that Sonny is vicious, psychotic, and clever. Sonny convinces Luisa to drug Kathrine into insensibility again so that he and Luisa can control her fortune. Sonny uses Kathrine's attraction to him to revenge himself on Luisa for her infidelities (real and perceived) and to exercise control over Kathrine, but the situation twists when Luisa joins the bedroom fun. The fundamental insanity of the characters builds the pressure on the three-way dysfunctional relationship until everything explodes in a shockingly violent climax.