Mr. Sin closes in on Leela, who snatches up a carving knife. She throws it into the dummy but it’s unaffected. Meanwhile, Chang takes the unconscious Litefoot’s gun and hears the Doctor approach. He prepares to shoot him. Inside, Leela leaps out the window. The Doctor, alerted, ducks and Chang misses. The magician escapes with Mr. Sin on their carriage. While the Doctor goes inside, Leela ignores his orders to stay and leaps onto the back of the carriage.
The Doctor tends to Litefoot and wonders what they might have been looking for. The Doctor notes an ornate Chinese cabinet and Litefoot explains that no one has been able to open it. The Doctor realizes it’s advanced technology and believes it’s connected to Weng-Chiang.
Leela enters the Palace Theatre and follows Chang into the sub-cellar. Weng-Chiang, cutting up meat for his rats in the sewers, demands answers. Chang insists that he hasn’t failed and they will recover the Time Cabinet the next day. Weng-Chiang isn’t convinced and laments his fate, trapped beneath the ground. He warns Chang that the Doctor knows he’s there now and will be back. Weng-Chiang says he needs strength to move when necessary and reminds Chang to fulfill his promise to bring him two young women. Chang goes out to find victims and Leela follows him.
The next morning, Litefoot wakes up to discover the Doctor charting the course of the sewers from the Thames to the Palace Theatre on a tablecloth. Once the Doctor is done, Litefoot takes the tablecloth out to the laundry basket. The Doctor asks if he has an elephant gun and Litefoot shows him a fowling piece. The Doctor then asks him to find a boat so he can enter the sewers.
Leela follows Chang as he stalks a prostitute and mesmerizes her. He commands her to come with her and she mindlessly obeys. Leela follows them back to the theatre where Chang leaves the woman, Teresa, in his dressing room. He hears cleaning women in the theatre and goes after one of them. Meanwhile, Leela’s unable to bring the girl out of the trance and switches clothing with her. Chang takes her and a mesmerized cleaning woman to the sub-cellars.
The Doctor and Litefoot approach the confluence in a boat and they find the sewer entry.
Chang takes the two women to Weng-Chiang and warns that he took one of them from the theatre. Weng-Chiang is unconcerned, saying once he has the Time Cabinet he can leave. Chang places the cleaning woman in the distillation chamber and leaves.
The Doctor proceeds alone on foot into the sewers.
As Weng-Chiang activates the distillation chamber, Leela advances on him. The cleaning woman’s life force is stripped away as Leela tries to strangle Weng-Chiang. She tries to shut down the machinery but fails, and the cleaning woman is killed. When Leela tries to climb up the ladder, Weng-Chiang fires an energy pistol at her. She’s forced to flee into the sewers and Weng-Chiang seals the entrance behind her and summons his giant rats.
Chinese laundrymen arrive at Litefoot’s house and drop off a basket, taking the old one.
Teresa wakes up from her trance and Casey spots her as she comes downstairs. As he tries to get her out, Jago arrives and Teresa recognizes the post of Chang and insists he was responsible for her abduction. Jago assures Casey that he’ll relay everything to the Doctor, who he believes is a high-up gentleman assisting Scotland Yard. Chang overhears the conversation.
Leela runs through the sewers and the Doctor follows the noises.
Weng-Chiang tells Chang what happened and the magician worries that the police are closing in. His master tells him he has made too many mistakes and until he has the Time Cabinet, he can never be whole again. Weng-Chiang dismisses Chang from his service but Chang promises to strike down the Doctor. Once Chang has gone, Weng-Chiang transfers the cleaning woman’s energy into himself.
Leela runs through the sewers with the giant rat in hot pursuit. The Doctor hangs up the lantern and prepares to shoot. Leela rounds the corner but as the Doctor prepares to shoot, the rat grabs her leg and starts to pull her back…