The blue crystal that the Doctor took from Metebelis III in a previous adventure is desperately sought by the Eight Legs, a race of mutated spiders, as the final element in their plan for universal domination. With help from an old mentor, the Doctor realises the only way to foil the plot is to make the ultimate sacrifice. The Doctor must risk death to return to the cave of the Great One and save the universe.
The Master, an old adversary of the Doctor, has arrived on Earth to destroy humanity with the aid of the Nestene Consciousness and their army of Autons and killer plastic daffodils - unless the Doctor, joined by new assistant Jo Grant, can stop them.
On Earth in 2018, the Doctor and his companions are enmeshed in a deadly web of intrigue thanks to his uncanny resemblance to the scientist/politician Salamander. He is hailed as the "shopkeeper of the world" for his efforts to relieve global famine, but why do his rivals keep disappearing? How can he predict so many natural disasters? The Doctor must expose Salamander's schemes before he takes over the world.