TARDIS brings the new Doctor, Polly and Ben to the planet Vulcan. The Doctor witnesses a murder and, investigating the body, discovers a pass badge allowing him unrestricted access to the colony.

Posing as an Examiner from Earth, the Doctor warns the scientist, Lesterson about the dire consequences of reactivating the dormant Daleks.

Polly is taken prisoner by the rebels who intend to use the Daleks to take control of the colony. The Doctor discovers that all three Daleks have now been reactivated.

Lesterson is driven insane when he discovers that the Daleks are reproducing themselves, and are preparing to seize control of the colony.

Bragen leads the rebellion and takes control of the colony, killing Governor Hensell. But the Daleks are also ready to make their final move.

As a battle rages between the rebels and the loyal colonists, the Daleks begin their attack. The only chance of survival for the colony rests with the Doctor.