The late-Victorian era provided aficionados of detective fiction with an abundance of short stories belonging to this literary genre. Many of these works contained some aspect of chemistry, either in the execution of a crime or in the identification of the perpetrator. In the example discussed in this article, the gas-phase reaction of hydrogen and chlorine plays an important role as the plot unfolds. Other chemistry related topics, including the use of a gas-filled balloon, the instability of nitrogen chloride, and the effects of the drug narceine, also enter into the story. (Contains 1 figure.)