Within a desolate Cornish landscaping full of relics of prehistoric man, the doctor and Evelyn uncover a catalogue of mysteries. What is the secret from the fogou? Can the moor end up being haunted by a demonic web host of imps? And what’s Brigadier Lethbridge-Stewart carrying out in Pengriffen? Teaming up with his previous friend, the physician realises that an ancient conflict is nearing its bottom line – and Lanyon Moor is defined to be the ultimate battleground.