""The Green Man"" - icon of the Celtic faith - is murdered. His daughter Morwenna asks Home Guard sergeant Ben Oakley, a retired detective, for help. Despite his being committed to organising a secret army in case of the anticipated German invasion, together they unmask the killers but in so doing, they discover a spy ring and Ben comes to realise that the idyllic Somerset village in which he lives is the epicentre of the secret Pagan world...