On the way to show Brighton to Leela, the TARDIS lands on the island of Fang Rock off the south coast of England in the early 20th century. Noticing that the lighthouse isn't functioning properly, the Fourth Doctor decides to investigate, as well as to ask for directions, as the TARDIS seems to have got 'lost in the fog'. Upon arrival at the lighthouse, and after introducing themselves, the Doctor discovers the dead body of one of the keepers, Ben. The other two keepers, old superstitious Reuben and the keen young Vince Hawkins, report that a light fell from the sky near the island. They also explain the electricity flow to the lamp on the lighthouse has become erratic and the Doctor deduces something is feeding on the flow. Reuben does not help matters with his constant references to the mythical Beast of Fang Rock, which reputedly once terrorised the lighthouse. As the Doctor and Leela explore, something moves Ben's body out of the lighthouse and onto the island, and they witness a curious electric crackling which seems to have killed fish nearby.