The TARDIS brings the Doctor, Jamie and Victoria to the south coast of present-day Earth. Something nasty is lurking in the gas pipelines of the North Sea, and before long the nearby refinery is under attack. Landing on a foam-covered beach, the travellers are at first mistaken for saboteurs. A number of the refinery personnel have been behaving strangely, and the base chief, Robson, is showing serious signs of stress. Meanwhile Maggie Harris, having been stung by a mysterious frond of sea vegetation, is menaced by the sinister engineers Oak and Quill.

The TARDIS lands in 22nd century Africa in the shadow of a dormant volcano. Agri-teams are growing new foodstuffs in the baking soil to help feed the world’s starving millions – but the Doctor and Rose have detected an alien signal somewhere close by. When a nightmare force starts surging along the dark volcanic tunnels, the Doctor realises an ancient trap has been sprung. But who was it meant for? And what is the secret of the eerie statues that stand at the heart of the volcano?

On a lonely stretch of Welsh coastline a fisherman is killed by a hideous creature from beneath the waves. When the Doctor and Rose arrive, they discover a village where the children are plagued by nightmares, and the nights are ruled by monsters. The villagers suspect that ancient industrialist Nathanial Morton is to blame, but the Doctor has suspicions of his own. Who are the ancient figures that sleep in the old priory? What are the monsters that prowl the woods after sunset? What is the light that glows in the disused lighthouse on Black Island?

The year is 1986, and at the South Pole the crew of the Snowcap Base have detected a new planet on their radar. The arrival of the Doctor, Ben and Polly at the Base coincides with another landing - that of a spaceship whose humanoid passengers have used cybernetics to replace their limbs and vital organs.