Brinley Knight is an agent with MI5.
The period of time we first encounter this operative is 1937 as Britain struggles with the prospect of war with Germany; many in the government strive to maintain some semblance of peace through appeasement while others work to prepare for what they consider an inevitable conflict. Tensions in the United Kingdom were extremely high as many wanted their leaders to stand up to Hitler and keep hims expansionistic plans at bay while many others, especially like-thinking fascists, of which there were a good number, wanted the government to embrace the tenets of the Germans, oust the Jews from England, and vow to never take up arms against its Teutonic cousins.
It is in April of that year we first meet Knight as he and his friend, mentor, and supervisor, Charlie, have just completed a three-week auditing job at the British subsidiary of a major German corporation. Knight was an accountant at the time and was not consciously looking for a change of employment though very long days of pouring over account ledgers did take a toll. Even with someone with a photographic memory as Knight has gets blurry-eyed staring at numbers for long hours at a time. Tack on the fact that Knight had soured considerably after dealing with the often humorless German company leaders.
It would be this audit and the discrepancies they had uncovered which would lead to Knight changing careers and becoming an operative with MI5 - that and a gunshot out in the street leaving a pub with Charlie and seeing a bullet hit his friend just above the bridge of his nose. A second bullet came and then a third as the unseen gunman tried to eliminate Knight as well and only luck kept him from joining his colleague in death. Yet another bullet would end that lucky streak but leave Knight still alive with a graze to the head and a concussion and a determination to find who had assaulted them and get justice for Charlie. And to prove people at that company were calling the shots. One of the first people to show up asking questions was an MI5 operative also looking into the German company and through him, Knight would see his new line of work beckoning.
We learn soon of Knight's political views and "his desire to help defend the nation from communists, fascists and foreign spies. Extreme right and extreme left politics had always disturbed him. They hated the sort of liberal democracy he wanted to flourish in Britain, and every day he saw the threats to his country, both militarily and politically, grow more dangerous." Working for MI5 against the enemies of the country sounded like just the thing for this handsome, glib, sociable young man who secretly craved excitement.
He kept his determination to make a go of working for MI5 even after an experienced operative, Sam, the man who first interviewed him, admitted, "We are depraved creatures here [at MI5]. There are no depths we will not go to in order to catch a foreign spy or British traitor. We do what we must to protect this country, and we do not apologize to anyone for the actions we take. This section is under tremendous strain. We have barely enough funds to keep our doors open". Knight saw no problem with any of that.