Polly Cameron is rushed to hospital where she dies of a mysterious illness. The doctor doesn’t know why. Lynne Cameron (Jean Peters) is Polly’s step-mother. She has been caring for Polly and her brother Doug (Freddy Ridgeway) ever since their father died. Whitney “Cam” Cameron (Joseph Cotton) is the children’s uncle. Lynne had been married to his brother. Cam holds great admiration for Lynne. She had been raising the children by herself after the death of her husband.

One evening Cam is visiting his brother’s lawyer, Fred Sargent (Gary Merrill), and his wife Maggie (Catherine McLeod). Maggie mentions Polly’s symptoms sounded familiar to her. She says that Cam’s brother had similar complaints before he died. Maggie also writes murder stories for magazines. She checks the symptoms in the encyclopedia and finds that they mimic those for strychnine poisoning. Cam is aghast that Polly may have been poisoned. He says there is no reason for it. Fred points out that Cam’s brother had his estate put into a trust. The children were living off the interest of that trust. Lynne could only inherit if both children died.

Cam doesn’t believe that Lynne could do such a thing but he decides to tell the police and have an autopsy done on Polly. The autopsy shows that Polly died of Strychnine poisoning. An investigation is launched and Lynne is suspected. Cam’s brother’s body is exhumed but no Strychnine is found. Still the police know that Polly was poisoned and Lynne has a motive and opportunity. She is brought to court but there isn’t enough evidence to charge her.

In the meantime Lynne tells Cam that she will be taking Doug on a trip to Europe. In fear for his nephew, Cam decides to take the same cruise so as to keep an eye on Lynne. Trying to hide that he suspects Lynne, Cam starts romancing her. On the last night of their cruise Cam decides he must take desperate steps to save Doug. Cam decides he needs to kill Lynne.

“A Blueprint for Murder” was released in 1953 and was directed by Andrew L. Stone. It is a crime/drama with film noir elements. The film is a fast paced thriller. There are twists and turns but they are mostly emotional, did she, didn’t she, she couldn’t, she could. As with many noir style films the emotional rollercoaster is part of the plot.

There is some mystery in whether or not Lynne did kill her step-daughter, but not a lot. Even though her husband had similar symptoms, there was no evidence that she killed her husband. Therefore no true pattern of murder for gain. She does remark that Doug doesn’t look healthy. She intimates that he is getting sick. This would paved the way should something actually happen and Doug does die for some reason. Still she appears to be affectionate toward her step-son and interested in his welfare. Then again many sociopaths are good at mimicking emotion when the occasion calls for it.

Cam’s psychology is also interesting. At first he has high regard for Lynne. He believes she is a good mother to the children and is loving and caring. When Maggie broaches the subject of poison he is incredulous. Being pragmatic he agrees to find out for sure what happened to Polly. When murder is discovered he is willing to suspect Lynne but he wants all the facts in before totally believing she is a murderer. When he finally does he is still in such a miasma of how to stop this woman that he is willing to contemplate murder himself.

The model of the cruise ship in the film is the same one used for “Titanic” (1953), “Gentlemen Prefer Blondes” (1953) and “Dangerous Crossing” (1953). The interior views of the dining room and staircase were from these movies as well.