The narrative follows a forensic investigation led by a skilled scientist and his assistant, who are approached by an eccentric gentleman, the director of a home for cats. He presents a peculiar mystery involving a donation box containing empty purses and an aluminum case filled with live fleas and dead lice. The protagonist, intrigued by the oddity, decides to investigate further. As the investigation unfolds, the scientist examines the items and hypothesizes about their origin and purpose. He notes the unusual presence of rat fleas and the scent of aniseed, suggesting a connection to rats. The narrative shifts to a separate case involving a bank manager who reports an attempted arson involving a deed box that turned out to be an incendiary device. The manager suspects a connection to a series of similar incidents across the city. The scientist begins to draw connections between the two cases, focusing on the potential for a criminal mastermind using fleas and lice to spread disease. He theorizes that the items found in the donation box may be part of a larger scheme to disseminate plague and typhus through infected insects. The investigation leads them to a street performer in a squalid area, who exhibits performing rats. The protagonist suspects this individual may be linked to the arson case. Through careful observation and deduction, the scientist uncovers that the performer is indeed involved in a nefarious plot to spread disease. The investigation culminates in a raid on the performer's residence, where they discover evidence of the man's criminal activities, including a sick individual infected with typhus. The scientist's meticulous work reveals the connection between the flea and lice donation and the broader implications of public health threats. Ultimately, the narrative concludes with the scientist's successful identification of the perpetrator and the prevention of a potential outbreak, highlighting the intersection of science, crime, and public health. The story emphasizes the importance of observation, deduction, and the application of scientific methods in solving complex mysteries.
By R. Austin Freeman · First published 1910 · Genre: Mystery, Detective Fiction, Thriller