Little Alfie of the Baker Street Irregulars seeks the help of Holmes and Watson as his cousin Flora has been arrested and accused of a double murder. The investigation gets underway with a trip to the scene of the crime.
Holmes is suspicious and, together with Watson, he travels incognito to The Imperial Gasworks. Their visit is both informative and productive involving a little deception and some slight of hand by Watson to obtain some Rattle-Jacks.
The postmortem confirms Holmes suspicions but he now has to gather sufficient evidence to convince the Coroner and the jury that this is not in fact a case of murder.