This is Leonard Mosley's amazing book The Druid (1982) which is a historic novel about a Nazi spy who double-crossed the famous Allied double-cross system and was thus never caught by the British counter-intelligence. Officially, the Nazi attempt to infiltrate England failed. Officially, all the Nazi operatives were caught and killed, or turned into double agents to serve the Allied cause. All but one. The man British Intelligence would like to forget. The man whose reports came within a hair's breadth of destroying the D-Day invasion and who almost cost the Allies the war. The man who can lay claim to being the single most brilliant spy of World War II - wherever he might be today. He was motivated against the British because of his ethnicity (Welsh) and had a natural ability to blend with the British society. The Druid is a gripping story based on historical facts of a man they said could never be. 255 pages. A must read for everyone.