Vincent Price stars as Dr. Chapin, a scientist who discovers a caterpillar-like parasite that grows in the human spine when someone is afraid. Unless the victim screams, the parasite can grow large enough to be deadly. He solemnly dubs this creature the tingler. The owner of a nearby cinema befriends the doctor.
His deaf-mute wife suddenly receives all sorts of shocks, like the sight of a bathtub full of blood with a hand reaching out from it. Since she can't scream, she dies, and Chapin gets his hands on her oversize tingler.
When it eventually escapes inside the movie theater, the film within the film, and then the film itself, stops for an announcement from Price, out of character, urging the audience to scream their heads off.