THE TINGLER

A pathologist, Dr. Warren Chapin, discovers that the tingling of the spine in states of extreme fear is due to the growth of a creature that every human being seems to have, called a "tingler," a parasite attached to the human spine. It curls up, feeds, and grows stronger when its host is afraid, effectively crushing the person's spine if curled up long enough. The host can weaken the creature and stop its curling by screaming.

Movie theater owner Oliver Higgins, who shows exclusively silent films, is an acquaintance of Dr. Chapin. Higgins' wife, Martha, is deaf and mute and therefore cannot scream. She becomes quite nervous even at the sight of blood, which triggers her nervousness when Warren accidentally pricks himself. It gives Chapin the idea that she may very well be likely to have a visible Tingler to examine in her due to her inability to scream. He keeps this in mind while returning to his wife Isabel, who he lives with along with her sister Lucy. While Warren and Isabel have a rocky marriage due to Warren believing that Isabel is unfaithful, he uses her for a test of his theory about the Tingler by spooking her into believing he will shoot her dead. When he shoots her, she faints, which gives Warren the chance to X-ray her spine that reveals the form of the Tingler, which resembles a centipede.

Later on, David presents Warren with a new drug that apparently has a significant effect on the nervous system in lysergic acid. Warren, in an attempt to try out the drug to induce fear in himself, although he eventually is triggered to scream. After he recovers, he goes to the movie theater to look at Martha and her nervousness. He gives her an injection while telling Higgins about a prescription for barbiturates. Later that night, Higgins starts to see weird, apparently supernatural events appear in her room. She dies of fright. During her autopsy, Chapin removes a tingler from her spine. Isabel tries to use the creature to kill Warren by letting it out but Lucy, arriving home at the same time the creature is at the neck of Warren, screams, which stops the Tingler from moving, although it is established that it cannot be killed by conventional methods, which suggests that the death of the person leads to the demise of the Tingler in it. Chapin plans to not reveal the Tingler to the scientific public and instead wishes to put the Tingler back in the body of Martha.

After they contain the tingler and return to Higgins' house, it is revealed that Higgins is the murderer; he frightened his wife to death, knowing that she could not scream because she was mute. The centipede-like creature eventually breaks free from the container that held it and is released into the theater below the house. The tingler latches onto a woman's leg, and she screams until it releases its grip. Chapin controls the situation by shutting off the lights and telling everyone in the theater to scream. When the tingler has left the showing room, they resume the movie and go to the projection room, where they find the tingler and capture it.

Guessing that the only way to neutralize the tingler is to reinsert it inside Martha's body, Chapin does so. After he leaves, Higgins, who has admitted his guilt to Chapin, is alone in the room. As if by supernatural forces, the door slams shut and locks itself, and the window closes, echoing what happened just before Martha was frightened to death. The tingler causes the body of Martha to rise from the bed, staring at her husband. Higgins is so terrified that he is unable to scream. The screen fades, and Dr. Chapin's voice says, "Ladies and gentlemen, just a word of warning. If any of you are not convinced that you have a tingler of your own, the next time you are frightened in the dark... don't scream."

The Tingler escapes into a movie theater, causing panic until the audience is told to scream, which subdues the creature and brings the film to its close.

The ending blurs the boundary between film and audience, with Dr. Chapin (and Castle himself) addressing viewers directly, making their screams part of the resolution. It underlines the film’s central theme: fear must be released, not bottled up, or it can destroy you. The finale is both a narrative resolution and a playful, participatory stunt that cements Castle’s reputation for showmanship.