Dr. Priestly is a professor whose hobby is "the mathematical detection of crime". In this story, he must convince the police inspector that the man he plans to accuse of murder is, in fact, innocent.
The resolution of the mystery is not especially mathematical, only logical. Priestly is constantly reminding the inspector (and his Watsonlike sidekick/narrator) that he "most strongly deprecates all conjecture". When the inspector begins to tell him about how he believes the murder was committed, Priestly interrupts and says:
(quoted from The Elusive Bullet)
[M]y interest in these matters is purely theoretical, and confined to the process of deduction. You are beginning your story at the wrong end. If you wish me to listen to it, you must first tell me the full facts, then explain the course of your investigation, step by step.

(I guess I can see how my students might get a similar impression of me. Like most math professors, I am very insistent that they show me the process by which they derived their answer, and that this process is more important than the answer itself. )
Priestly is very confident in his superior intellect, and not afraid to insult others by expressing it. Even though he is not using what one might normally be considered mathematics in solving the crime (except perhaps for some elementary geometry), his mode of thinking is described as being mathematical:
(quoted from The Elusive Bullet)
"Very puzzling, very!" he muttered. "There must of course be some explanation. A mathematical deduction from facts can never be false. But I wish I could discover the explanation."

This short story is only one of a series of stories and books about Dr. Priestly, a detective reminiscent of Sherlock Holmes, written by Cecil John Charles Street under the pseudonym "John Rhodes". I have not yet had a chance to read any of the other works about this character, but would be grateful for feedback from visitors to this Website who may be able to inform me whether any of them should also be listed here.
