Disturbed by the idea that her daughter might be the one behind all these tragedies, Christine begins investigating and discovers she was actually adopted by her own parents: her birth mother, Bessie Denker, was a notorious serial killer who died in the electric chair.

As her mental state deteriorates, Christine begins writing letters to her husband discussing Rhoda, blaming herself for passing the “bad seed” gene to their daughter.

The only other adult aware of Rhoda’s true nature is Leroy Jessup, the maintenance man who works and lives at the Penmarks’ apartment complex, who relentlessly teases the girl regarding Claude’s death.

Afraid he will expose her, she waits until Leroy is asleep before lightning his mattress ablaze and locking him inside his shed; a horrified Christine witnesses the murder from afar.

Psychologist Robert D. Hare, who argues that the evidence suggests psychopathy is an inborn trait, discusses The Bad Seed in his 1993 non-fiction book Without Conscience.

A lengthy quote from the novel opens Hare's book, describing in March's words how most decent individuals are not by nature suspicious and thus unable to understand or anticipate the acts of evil and depravity that some people are capable of committing.

Later in his book, Hare argues that March's novel is a "remarkably true to life" portrayal of the development of psychopathy in childhood, illustrating both Rhoda's callous use of others to serve her own ends as well as Christine's growing helplessness and desperation as she realizes the extent of her daughter's behavior.

Rhoda is suddenly struck and killed by lightning when she goes back to the scene of her crime to retrieve the medal (allowing an interpretation of divine intervention), while Christine survives her suicide attempt.

During the closing credits, LeRoy added a light-hearted sequence of Nancy Kelly, Christine, holding Patty McCormack, Rhoda, over her leg and spanking her –possibly to remind audiences that this is just a movie.

[8] This version of The Bad Seed first ran on Lifetime on September 9, 2018, and was watched by 1.87 million viewers, placing it in the top ten most-watched cable programs on that date.