Mortimer Tregennis is a character in 'The Adventure of the Devil's Foot'. He lives in Tredannick Wollas, Cornwall, and lodges with the town vicar, Mr Roundhay, at whose urging Tregennis agrees to consult Holmes. He states that the previous night, he had visited his siblings, with whom he had recently reunited after a long and bitter dispute. He claims that he left them in perfect health and high spirits, but that they had been found at the same table the next morning, with his sister, Brenda, dead and his brothers, George and Owen, both mad. The day after his visit to Holmes, Tregennis is found dead the same way as his sister. A visit by African explorer Dr Leon Sterndale clears up the matter; Tregennis stole some powdered Devil's-foot root from Sterndale, from whom he had learned of its existence and poisonous effects originally. Sterndale, deducing Tregennis's guilt in the murder of Brenda Tregennis (with whom he was madly in love), held Tregennis at gunpoint and forced him to inhale the same toxic smoke, killing him. Holmes allows Sterndale to go unpunished for Mortimer Tregennis's murder due to the latter's guilt, telling him to return to Africa permanently.
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