Department Z is a British Intelligence agency.
In the early 1930's, the government of Great Britain knew it needed an organization that could help in the troubling international times ahead. War was brewing too quickly and spies and trouble-makers were everywhere. The official groups, such as the Special Branch, were equipped to handle the majority of cases but once in a while there were events too strange or too sensitive to leave to a group so well known.
The answer was Department Z, an ultra-secret collection of 'civilians' who could work the dark alleys and back rooms without publicity. To head that hush-hush division, the government looked to Gordon Craigie.
In the many years, before, during and after the Second World War, the men of Department Z fought the enemies of the Crown no matter where they were found. Be it the corridors of Whitehall, the mansions of the countryside, or the fields of foreign lands, the many dedicated men of Department Z served their country and their leader, Craigie, with distinction for a quarter century.
Officially, the members of Department Z were civilians and therefore the government was able to deny much of their activity. Nevertheless, when the troubles came, the men could call upon many of the resources of the nation, secretly, of course.
It was a solid rule throughout the life of the department that only single men need apply. Worried that the concern of a spouse or children might keep a man from giving a mission his all, Craigie followed the tenet of unattached only throughout. This included the forced retirement of his key agent, Jim Burke, as well as other, lesser known agents.
When Pyramid and Arrow both elected to republish the books in paperback format, whether separately or as a concerted effort, John Creasey took the opportunity to modernize the stories somewhat. He indicated it was to smooth things out a bit but in the smoothing some changes were made and possibly an inconsistency or two snuck in. Nevertheless, the stories do not suffer.