- "It was Claude Daigle who drowned. Not me."
- —Rhoda Penmark (not seeming to understand the significance of her classmate's murder)
Rhoda Penmark is the villain of the 1954-published novel (and later, 1956-released film) The Bad Seed. She is a sociopathic eight-year-old girl, whose evil tendencies are genetically inherited.
She was portrayed by legendary actress Patty McCormack the 1956 film.
When her classmate Claude Daigle wins the penmanship award she feels she should've won, instead of congratulating him, she viciously attacks him with her tap shoes. Afterwards, she drowns him in a nearby lake.
Although she suspects that her little girl is not quite normal, Rhoda's mother, Christine, dismisses the idea that her daughter was involved in the little boy's death in any way. Rhoda herself is completely untroubled by Claude's death, and just carries on as though nothing happened.
The only adults who can see Rhoda for what she really is are Leroy (the mentally-handicapped janitor employed by Rhoda's parents) and - to a lesser extent, at any rate - Rhoda's school teacher, Miss Fern. Miss Fern sees that the girl is a very bad loser and is highly selfish.
Leroy spies on Rhoda, and threatens to tell on her time and time again, only for her to call his bluff and say that no one would believe him. However, despite her claims, Rhoda has her own fears - and starts trying to get rid of Leroy.
Christine, meanwhile, tries to relieve her fears about her daughter, by talking about Claude's murder to her adopted father and Mrs. Breedlove - a neighbor who takes an interest in psychiatric theories about personalities.
That same night, Claude's mother turns up at Christine's home, drunk. She tells Christine that something is amiss, and tells Christine that she should ask Rhoda about her last moments with Claude.
While Christine is looking for Rhoda's necklace - which Mrs. Breedlove is engraving for her - she discovers the Penmanship Medal in Rhoda's treasure chest. Initially, when confronted by Christine, Rhoda denies any wrong-doing. However, after Christine discovers Rhoda's blood-stained tap-shoes, Rhoda - not seeming to understand what the problem is with the situation - confesses all.
While Christine is wrestling with her conscience - trying to figure out what to do - Leroy searches the incinerator for the tap shoes, Rhoda locks him in and burns the incinerator - thus, burning Leroy alive.
After learning what her daughter has done, Christine ends up having to try and kill Rhoda, by giving her a lethal dose of sleeping pills - before then trying to kill herself.
In the original novel and the stage play, Christine actually does kill herself: however, in the movie, she survives.
In the novel and play, Rhoda survives - after being taken to the hospital: she is later free to kill again. However, in the movie, she dies after being struck by lightning. She snuck out in a rain slicker, and went out to try and find the medal out in the lake, where Christine said she disposed of it earlier.