Three crooks walk out of court as free men. Regan is determined to get a conviction, and plans to make one of them turn Queen's evidence.
With Jo held prisoner in his TARDIS, the Master forces the Doctor to take him to the underground city of the primitives. Any sign of treachery from the Doctor and Jo will die.
In the underground city, the Doctor and the Master confront the guardian of the doomsday weapon. The miners make their last move to force the colonists to leave the planet.
The Master arrives, posing as an adjudicator from Earth who has come to settle the dispute between the colonists and the miners. However, the Master has an agenda of his own.
When Jo attempts to break into the IMC ship to find incriminating information, she is captured and held hostage. If the Doctor doesn’t cooperate, Captain Dent will have Jo killed.