Sir Ernest Pease KBE FRS (James Robertson Justice) is a cantankerous and crotchety old professor. Testing one of his new radar inventions (and travelling incognito as Lt. Farrow, RN) the plane he is travelling is shot down and he is incarcerated as a POW. His overbearing and abrasive manner leads his fellow inmates into believing he is a german spy, but when they discover who he actually is they realise that his escape is vital to the war effort.