Dr. Chapin (Vincent Price) and his faithful intern David (Darryl Hickman) discover a parasite that grows bigger and more dangerous when the host individual becomes terrified. When the creature escapes to a silent movie theatre, individuals are in jeopardy unless they scream as loudly as possible, which drives the parasite away from the backbone where it can be comfortable. Because a mute victim (Judith Evelyn) cannot scream, she is the perfect host for the monster. Complicating matters is Dr. Chapin’s nasty tempered wife Isabel (Patricia Cutts) who may impede science over her unhappy marriage. Isabel could end up as part of the experiment to cure people of the Tingler parasite.