When a body is found in London's most celebrated Turkish bathhouse, the detectives must hunt down a killer targeting gay men. But the investigation puts strain on their relationship when Theodore reconnects with an old flame.

It's the Turbulent Thirties. 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.