Penny is a makeup artist in 1950s Hollywood, who has just been dropped by her sexual partner, Mr. D, and has moved into a new bungalow. Almost immediately, she senses that something is amiss in her unit. At night, she hears a tapping sound and thinks there is something -- little men, or mice, who are living in her walls. She soon meets her neighbors, Benny and Mr. Flant, who tell her that a previous tenant in the unit, Larry, died by suicide there some years ago. She begins to feel more unsettled in the house. Benny and Mr. Flant tell her that Mrs. Stahl, her landlady, loved Larry. In the meantime, Penny is trying to get one last check from Mr. D, who owes her some money. She sends him a threatening letter and loses her job as a makeup artist.

Penny suspects that Mrs. Stahl may have killed Larry. She meets her one night, out in the courtyard, and she invites her to her own home. Penny thinks that Mrs. Stahl drugged her when she wakes up the next morning still in Mrs. Stahl's home. She takes her teacup -- and a book that Mrs. Stahl has, from Larry, which calls Mrs. Stahl a "murderess" -- to a detective, and tells him to check out Mrs. Stahl. He dismisses her fears.

Benny comes over to her bungalow, where she has been smelling gas, to check out the oven. He freaks out when he sees something behind it, and they rush him out. In a blur, the rest of the action happens: she knocks into Mrs. Stahl in the courtyard, likely killing her, and then goes back into the bungalow. She looks behind the stove and lights a match to see what Benny saw: a suicide note from Larry about little men. Lighting the match catches all the gas in the apartment on fire, and it blows up. The same detective who dismissed her investigates the case.