Elderly landlady Mrs Beck is appalled to discover the gentlemen detectives in flat #4 are more than just business partners. But when a man is murdered in the building, she is forced to ask for their help.

It's the Roaring Twenties. Homosexuality is a crime in Britain, yet London is home to a thriving queer underworld. But when your very existence is a crime, who can you trust if not the police? Hugo Fox and Theodore Bellamy are partners, in life and business. Together, they run the Piccadilly Detective Agency, helping any innocent queer folk who cannot turn to the police, whilst also keeping their own relationship a secret.