It is the turn of the century and the Tardis materialises by a lighthouse on the desolate isle of Fang Rock. When a lighthouse engineer dies in mysterious circumstances, the remaining crew blame the mythical Beast of Fang Rock, that is until the Doctor and Leela turn up. When a small clipper runs aground the lighthouse offers shelter to its despairing passengers, but the Doctor soon discovers clues that suggest that no one is safe on the tiny island. He suspects a ruthless alien lurks in the thick unnatural fog that surrounds the island so he secures the lighthouse, but has he really locked the horror out, or is it somewhere inside with them? The doctor at his spooky best.