The Doctor is extremely concerned as he watches a televised archaeological dig near the village of Devil’s End in which a Professor Horner prepares to break into an ancient barrow.
Discovering that the Master has stolen their files on the devastating Doomsday Weapon, the Time Lords decide to use the Doctor to retrieve them.
An alien spaceship lands on Earth and in exchange for fuel, the crew offer a miraculous gift that could end global food shortages forever. But the Doctor has his suspicions.
At Stangmoor Prison, the Doctor and Jo observe a demonstration of the Keller Machine, a device which extracts negative and violent emotions from the minds of aggressive criminals.
The Master, a renegade Time Lord, comes to Earth and breaks into a museum where he steals a Nestene energy globe that was salvaged from their previous invasion attempt.