In 1961, an unpopular boy named Harold Rusk leaves a Valentine's Day card at the home of the beauty Susan Jeremy, [Barbi Benton]. Susan and her friend David mock and crumple the card, prompting an enraged Harold to break into the house and kill David by hanging him from a hatstand.
Nineteen years pass, and Susan is divorced with a daughter and a new boyfriend named Jack, [Jon Van Ness]. On Valentine’s Day, Susan has Jack take her to a hospital to pick up the results of a standard physical exam requested by her new health insurance. On the way inside, a man in surgical garb watches from a window and strokes a photograph of a young Susan, then sabotages the elevator she boards to delay her while he murders Dr. Jacobs, the doctor who holds her paperwork, which the killer also tampers with. A janitor later discovers Dr. Jacobs’ body and is gruesomely dispatched when the killer dunks his face in a sink of acid after trying to pursue him into a nearby storeroom.
While searching for her doctor, Susan convinces a kindly intern named Harry, [Charles Lucia], to fetch her results. Harry notices the paperwork looks abnormal and brings them to Doctor Saxon, [John Warner Williams]. The irregularities—made worse by the saboteur’s tampering after the deaths of two lab workers—lead Doctors Saxon and Beam to order that Susan be detained for observation. Harry uncovers evidence that someone is running a con game on Susan, but he disappears after vowing to set things straight. Jack, who had fallen asleep in his car while waiting for Susan, comes into the hospital to find her during her first escape and then waits nearby as the doctors reprimand her. The killer lures him to an empty hospital room by phone and, behind a curtain, Jack discovers the body of a nurse before the killer decapitates him with an electric orthopedic saw.
A large box is placed beside Susan’s bed and she opens it to find Jack’s severed head. Susan flees to seek help, and Saxon and a nurse locate her and return her to her room. When she tries to show them the box, it contains only a cake. After Susan recounts Harry’s findings, Saxon goes to inspect the archives and pull copies of her paperwork. She follows him, only to spot the killer heading toward the archives as well, armed with a surgical hatchet. In the archives, the killer waits in the dark and drives the hatchet into Saxon’s skull as he attempts to escape, then vanishes. Susan witnesses the scene from hiding, and her insistence that there’s a killer on the loose is dismissed as delirium, leaving her strapped to a gurney as doctors prepare for emergency surgery.
Nurse Dora, [Gloria Jean Morrison], is ambushed in an empty corridor, chased, and poisoned. Dr. Beam, [Den Surles], is stabbed through the neck from behind a medical screen while monitoring Susan’s X-rays. The killer abducts Susan and takes her to a vacant operating room. Susan removes the killer’s mask to reveal he is Harry, the intern, who is really Harold Rusk. When Susan asks what he wants, Harold replies, “What I’ve always wanted. Your heart.”
> What I’ve always wanted. Your heart
Before Harold can cut her open, Susan stabs him as he’s distracted by other patients and escapes. She races to the roof, where the wounded Harold sets after her, but Susan douses him with flammable liquid and sets him alight, sending him tumbling off to the street below. The next day, Susan is released and reunites with her daughter and ex-husband outside the hospital.
