The Turned Carpet

A stain on the rug, none on the boards beneath — measure the displacement that broke the case.

Blood soaks through: a stain above demands its shadow below. Enter the offset between stain and shadow, and read what the geometry confesses.

Drawn from The Adventure of the Second Stain (The Return of Sherlock Holmes, 1904) — read the summary & analysis, or try The Letter That Moved, this story's game. More at the Game Room and the tool bench.