Public opinion surveyor, or "Trotter" man, Pete Marshall arrives in Plainville, a town in the mountain district, to replace fellow Trotter man Hector P. Smedley, who disappeared after visiting the Fleagles, a family of gun-toting hillbilly outlaws. Upon entering the dilapidated house, Pete realizes that the crazy family has killed Smedley. Mother Mamie Fleagle Smithers Johnson, who goes by her third husband's name, rules her dim-witted grown twin boys, Mert and Bert, with a bullwhip, and orders Pete to pose for Grandma Fleagle as the "feller" of jailed robber Bonnie Fleagle. Grandma is dying of a poison that makes her glow in the dark, which was administered by Mamie's family, who are Fleagles by name only and are after Bonnie's $70,000 bank loot. Mamie hopes that Grandma will give Pete a clue to the whereabouts of the money. Before she dies, Grandma gives Pete a cross-stitched sampler on which is stitched a line of music to a nonsense song: "Flizon horzis, Beezin komzis, Onches nobis, Inob keezis." Claire Mathews, whose banker father has been linked to the robbery, poses as the escaped Bonnie and arrives at the Fleagles' to find the money in order to exonerate her father. The Fleagles try to poison her at dinner, but when the lights go out, all the plates are glowing except that of Mr. Johnson, Mamie's third husband, an eccentric scientist who developed the radioactive poison. Johnson disappears and is found dead. Meanwhile, Elany Fleagle, Mamie's lunatic young daughter, repeatedly sings the doggerel verses on the sampler, and a mysterious man who lurks in the shadows, whom she thinks is a ghost, frightens her into repeating the lyrics for his transcription. Claire locates Elany's room through a secret passageway and scares away the ghost, then finds the lyrics. The real Bonnie Fleagle arrives, after breaking out of jail, armed and determined to find the money. She decodes the first two lines with Pete's help, and later, Pete and Claire solve the rest of the riddle, which indicates a nob on a chest that contains a key to a safety deposit box. Claire and Pete get the key, and after a chase around the house, they are trapped in the hay barn by Bonnie, Mamie, Mert and Bert. They manage, however, to trap each in a bale of hay using a hay compression machine. Mr. Johnson, who is not dead, enters, and Elany, fearing he is the ghost who tortured her, pushes him also into the compression machine. Pete and Claire fall into the hay and emerge on the conveyor belt embracing in a bale of hay as the sheriff arrives.