Sherlock Holmes and Doctor Watson are summoned to Theobald Grange, the home of the overly-superstitious Lady Heminworth. Her Ladyship is on the brink of nervous collapse, a condition brought about by the recent murder of her husband and elder son, apparently by a man executed centuries ago. Now she is to be the next victim, and Holmes discovers that the motive originates with the banishment of her other son. His adversary seems unaffected by gunfire and is able to take flight and disappear, but Holmes knows that the threat is not supernatural.

Nevertheless, the killings continue...