A beautiful young heiress walks into the office of criminal defense attorney Perry Mason. She wants to get married, but a clause in her father's will threatens to leave her with only five thousand dollars if she marries before age twenty-five. Her wealthy uncle controls the trust, and he disapproves of the man she loves.

Mason takes the case, but soon finds himself in the middle of a murder investigation when the uncle is found dead. With the police focused on the chauffeur, Mason suspects someone else is responsible. He must unravel a web of family secrets, blackmail, and hidden motives to clear his client's name and find the real killer.