Mr. Watkins' narrates throughout the cartoon. Dorlock Holmes lives on Beeker Street in London. Inside of their apartment, Holmes is busily engaged in "deduction" — tax deduction, that is, hoping to write off such costs as "taxi fares, to and from murders". Following a knock on the door, a mailman falls into their flat. While Holmes attributes it to curare, a type of poison, the mailman chides him for not fixing the step. The letter says that there is a criminal on the loose named The Shropshire Slasher.