Inspector Alec MacDonald is a young, though relatively senior officer working for Scotland Yard. He consulted Sherlock Holmes about the murder of John Douglas at Birlstone House. Although initially skeptical that the case was connected with Professor James Moriarty, after Holmes showed that Moriarty owned an immensely valuable painting by Jean-Baptiste Greuze, one which he could not possibly afford on his professor's salary, MacDonald was very eager to listen to Holmes' opinions on the matter.