Devil's foot

Stories from the author's list '12 favorite stories about Sherlock Holmes'. Holmes and Watson go on vacation to the county of Cornwall. A few days later, they are visited by Mr. Mortimer Tregenis and Mr. Rhyndhey, who report that two of Mr. Tregenis' brothers have gone mad and their sister has died. Brenda died with a horrible expression on her face. After some time Mr. Mortimer Tregenis himself died, and so did his sister. Holmes examines the room and takes the lamp that was on the table in the dead man's room. When it was lit, the killing effect was immediate, well, Watson got Holmes out of the room in time. Holmes realizes that Mortimer Tregenis used poison powder to kill his brothers and sister, but who killed him? Translated by Mykola Dmytrenko.