The planet is Skaro, home-world of the Daleks.

The Daleks are excavating in order to find and revive Davros, the mad, crippled, scientific genius who first created them. They hope that he will give them the scientific superiority to break the deadlock with their Movellan enemies.

Faced once more with the deadly and seemingly indestructible Daleks, the Doctor's wits and strength are stretched to their very limits...