It shows development of tradecraft and the great personal risk officers and their agents took, far from home and unprotected. In Salonika, for example, Lieutenant Norman Dewhurst realised it was time to leave when he opened his door to find one of his agents hanging dismembered in a sack.
This first part of Six takes us up to the eve of the conflict, using hundreds of previously classified files and interviews with key players to show how one of the world's most secretive of secret agencies originated and developed into something like the MI6 we know today.