INTENDING TO TREAT LEELA TO THE DELIGHTS OF Victorian music hall, the Doctor is drawn into an investigation into the murder of a cabby whose mangled body appears to have been gnawed by an enormous rodent. The death is linked to the mysterious disappearance of nine girls; the most recent was the cabby’s wife Emma, last seen at the Palace Theatre. The shadowy figure of a reclusive masked phantom has been terrifying the staff of the theatre, much to the annoyance of its owner, Henry Gordon Jago.
The Doctor and Leela discover giant rats infesting the network of sewer tunnels beneath East London, the creatures acting as guards to protect a secret laboratory hidden under the theatre cellar. The Doctor soon deduces the involvement of stage magician Li H’sen Chang and the Tong of the Black Scorpion, fanatical followers of an ancient Chinese god named Weng-Chiang.