Private detective Paul Drake goes undercover as a prison convict to help Perry Mason develop the evidence needed to prove that his client, a prisoner at the penitentiary, did not call one of the guards.

Chance meeting with beautiful young girl leads Mason to become her defense attorney when she's arrested for murdering the brother of an aging architect who's been committed to a mental institution.

The kidnapping of Mason's young counsel Magic Larson from the courtroom complicates his attempt to gain a fair trial for a man accused of murdering a hated ranch foreman in a rural California town.