London 1930.

Selby Bigge and his aristocratic sidekick Theodora Smythe are invited to dine with Doctor Hector Fortescue and his family, discovering a web of unrest in the household. The good doctor is adamant that homosexuals can be 'cured' of their perversions, oblivious to the fact his son Lancelot is 'as fruity as a pineapple'. Later that evening Theodora becomes Theo and attends the Servants' Ball with Selby - a fancy-dress dance for servants, which attracts queers of all classes.

Lancelot makes a surprise appearance dressed as Harlequin, as do other members of the Fortescue household. And before the night is out Selby and Theo will have another murder to solve. Digging deeper, the duo - assisted by the impossibly glamorous nightclub singer Lady Splendid - discover that secrets abound both above and below stairs in the Kensington home of the Fortescue family.

And the stakes get even higher when Selby encounters policemen he's met before, who'd love to arrest him for being queer. Can Selby solve the crime or will this be his last dance?