A Blueprint for Murder is a 1953 American Film Noir thriller film directed and written by Andrew L. Stone and starring Joseph Cotten, Jean Peters, and Gary Merrill.
Two orphans, Polly and Doug, live with their stepmother Lynne; Polly collapses with the same mystery symptoms that killed her father. The kids' visiting uncle, Whitney "Cam" Cameron, is warned that the symptoms match strychnine poisoning, but that poisoners are seldom detected and rarely convicted. Sure enough, no case can be made against the obvious suspect; so what can Whitney do to save the next victim?
Tropes:
- Black Widow: Lynne fatally poisons her husband and stepdaughter, and attempts to poison her stepson in order to inherit her husband's entire estate.
- Gaining the Will to Kill: Having exhausted his legal options, Cam decides that the only way he can save his nephew Doug from his stepmother Lynne is to poison her. He balks at his first attempts and throws the poison overboard. However, on finding what he believes to be a poison tablet in her luggage, his will strengthens and he drops it into her cocktail.
- Medication Tampering: Lynne tampers with Polly's calcium pills to ensure that she receives a second fatal dose of strychnine while she is in the hospital.
- Romancing the Widow: Cam starts to fall for his brother's widow Lynne. He is initially romancing her because he is attracted to her, but continues to do so because he becomes convinced that she is a Black Widow and wants to prove it.
- Slipping a Mickey: Cam surreptitiously drops the tablet he believes to be strychnine into Lynne's Bacardi cocktail.
- Wicked Cultured: The Black Widow Lynne is described as "young, beautiful, intelligent and cultured" and plays classical piano like a virtuoso.
- Wicked Stepmother: Lynne murdered her husband and then plans to murder her two stepchildren because the will states that she receives the entire estate if the children die before they reach their majority.
- Would Hurt a Child: Lynne has no compunctions about poisoning her two stepchildren.
