A ball of fire falls into the ocean off the coast of England near Fang Rock. The three keepers of the light house are surprised when its arrival is followed by a thick fog and a sudden chill. Soon after, the electrical generator starts acting up. The Doctor and Leela arrive as something green slithers around on shore and kills Ben, the lighthouse engineer. The Doctor and Leela arrive in the lighthouse and find Ben's body. This draws the suspicions of Reuben, the elderly lighthouse keeper. Leela tries to hunt Ben's killer in the fog but it evades her and takes Ben's body. Just then, a steam yacht comes racing through the fog. Despite the horn and emergency flares, it crashes directly into the rocks amidst the terrified screams of its passengers.