Dunkirk, May 1940, with the French army retreating and the British army fleeing back to England...

SS Leader, Heir Himmler devises a plan to plant a German agent amongst the British troops and with limited help gives him carte-blanche to cause as much havoc as possible in England.

Meanwhile, in Scotland Yard, London, a counter-espionage team of Police Officers are making ready to combat this threat. Leading the team are ex-Rifle Brigade Sergeant, Dave Selby and ex-Rifleman Bill Auger - now DI Selby and DS Auger.