Episode One tells the story of the founding of the SAS in the heat of the North African desert in 1941. David Archibald Stirling is an aristocratic dreamer who had once held lofty ambitions to be an artist or perhaps a famous mountaineer, but now, with the war in the desert reaching its most desperate stage, Stirling has a vision for a new kind of war: attacking the enemy where they least expect it - from behind their own lines.

With the tragic loss of Jock Lewes, Stirling's second in command is now newly promoted Captain Paddy Mayne, an officer as unpredictable and dangerous as the new phase of war that is about to begin. Unbeknown to David Stirling, the Germans are training special units to track, intercept and kill the marauding SAS. The hunters will soon become the hunted.

Stirling is locked away in Colditz: Hitler's most secure prison. Leadership of the SAS passes to Paddy Mayne, a man who has built his reputation on the battlefield as a warrior of the first rank, however, unlike Stirling, Mayne has no interest in charming high command.