1941. Britain is under some of the heaviest air raids of the Second World War. Concerns about Nazi paratroopers landing in Britain and invading take hold in the hearts of the British citizenry. The Home Guard has been mobilised to defend against airborne assault - and it needs training. 'Yank' Levy is brought in to Osterley Park to teach guerrilla warfare, from practical experience in the Spanish Civil War. 'Yank' trains soldiers of the Home Guard how to use surveillance, defend against tanks and armoured vehicles, how to fight in towns and across country and against a well-supplied, highly-trained and mobile occupying force. His book, Guerrilla Warfare offers such sound advice as: 'Whether you go to a tea-party or to work on your allotment...take your rifle with you. Don't leave it downstairs for a German to grab if he enters the house' and 'Your motto should always be: 'Finish them! Then a quick get-away, and another ambush some place else''