In the summer of 1941, at the height of the war in the Western Desert, a bored and eccentric young officer, David Stirling, came up with a plan that was radical and entirely against the rules: a small undercover unit that would inflict mayhem behind enemy lines.

Despite intense opposition, Winston Churchill personally gave Stirling permission to recruit the toughest, brightest and most ruthless soldiers he could find. So began the most celebrated and mysterious military organisation in the world: the SAS.

Now, 75 years later, the SAS has finally decided to tell its astonishing story. It has opened its secret archives for the first time, granting historian Ben Macintyre full access to a treasure trove of unseen reports, memos, diaries, letters, maps and photographs, as well as free rein to interview surviving Originals and those who knew them.

The result is an exhilarating tale of fearlessness and heroism, recklessness and tragedy; of extraordinary men who were willing to take monumental risks. It is a story about the meaning of courage.