On the morning of 6 June 1944 - D-Day - Captain John Tonkin and Lieutenant Richard Crisp were dropped deep inside Occupied France. They were to lead an SAS troop to stop the German's bringing up reinforcements to repel the invasion.
Sabotage teams were sent out to blow up roads, railways and marshalling yards. But soon their camp was surrounded by 450 SS troops. Thirty captured men, under Lieutenant Crisp, were murdered under Hitler's notorious Kommandobefehl, ordering the summary execution of all commandos caught in German-held territory.
A second troop under Lieutenants Ian Stewart and Ian Wellsted operating further to the east had more success. They cut the main railway lines twenty-two times, derailing six trains and destroying three locomotives and some forty wagons.
Synthetic fuel plants were mortared. Power lines and telephone lines were downed. A dozen enemy airfield were reconnoitred for air attack. Thousands of maquis were armed and trained. Prisoners were taken and sixteen Allied airmen rescued.
Leaving German morale severally dented, Wellsted led the troop back to the advancing Allied lines, shooting up retreating German convoys as they went.
Behind Enemy Lines is the story of courage under fire - and how a few brave men made a difference during the Normandy landings.
Who dares wins.
Nigel Cawthorne is the author of over two hundred books. He lives in London.