The Doctor has no choice but to turn the parasite against the Master.
The Keller Machine is out of control so the Brigadier launches an assault on the prison.
The parasite within the Keller Machine becomes too powerful for the Master to control.
The Master plans is to capture a missile and launch it at the World Peace Conference.
A full scale riot takes place at Stangmoor Prison and Jo is taken hostage.
At Stangmoor Prison, the Keller Machine can extract evil impulses from criminals.