This is a mystery and detective novel that revolves around Mr. Fanks, who is also known as Octavius Rixton, an idler from the West End of London. Mr. Fanks leads a dual existence where he earns his money as a detective and spends it as a man about town. One evening, while going to a theatre, Mr. Fanks is approached by another detective named Crate, who informs him of a murder that has taken place in Tooley's Alley. Mr. Fanks quickly changes into his detective clothes and goes to investigate the murder. The murder victim is a gentleman who has been poisoned in the Red Star pub owned by Mrs. Boazoph, which is known for being a hangout for criminals. As Mr. Fanks investigates the case, he discovers that the victim had a tattoo on his arm. Is the tattoo the key to solving the murder mystery?
