Inspector Blair is still on vacation at his sister’s in England when a recent murder has him helping the local police. He knows the condemned man is innocent when he hears of the evidence of the gunshot wound.
Blair sets about describing the case, and why he knows they have the wrong man. What was the murder weapon? There were no bullets found, despite having an entry wound, but no exit wound. A second murder had a similar fatal injury, but the young man, Slade is off the hook since he was held in jail at the time. Who did it, and how are the crimes related?
There is a bullet that was found, but Blair shoots down the reasoning behind why it doesn’t fit as the murder weapon. An obvious conclusion if you think about the ballistics of how bullets travel.
The team of cops revisit the crime scene. Blair interviews the old professor who owns the estate. The professor is an expert in ancient weapons. The prof himself is nearsighted, and thus is taken out of immediate suspicion as a killer from all but Blair.
The professor has one last trick up his sleeve to keep from being taken alive by the cops. Blair explains all to the local cops, and lets them take credit for solving the mystery as he ducks out of the scene, just as the big boys from Scotland Yard approach.