The Doctor and the Master confront the guardian of the Doomsday Weapon.
The Master forces the Doctor to take him to the underground city of the primitives.
The Master pretends to have come to settle the dispute between the colonists and IMC.
When Jo attempts to break into the IMC ship she is captured and held hostage.
The Interplanetary Mining Corporation, led by Captain Dent, arrives on the planet.
The TARDIS takes the Doctor and Jo to the future where colonists are menaced by a monster.