Ernest Drabble, a Cambridge historian and mountaineer, travels to rural Devon to inspect the decapitated head of Oliver Cromwell - a macabre artefact owned by Dr Wilkinson. Drabble only tells one person of his plans - Harris, an old school friend and press reporter. On the train to Devon, Drabble narrowly avoids being murdered, only to reach his destination and find Dr Wilkinson has been killed. Gripped in Wilkinson's hand is a telegram from Winston Churchill instructing him to bring the head of Oliver Cromwell to London. Drabble has unwittingly become embroiled in a pro-Nazi conspiracy headed by a high-status Conservative member of the British government. And so, Drabble teams up with Wilkinson's secretary, Kate Honeyand, to find the head and rescue Harris who is being tortured for information.