Al Trelawney is an agent for the Department in British Intelligence.
This Department is an apparent independent section of the British Special Branch. Apparent because while Special Branch is mentioned in the opening page of the first book, it is always referred to as the Department from then on and its activities fell more in line with MI-6 than the traditional Special Branch. Whichever it is, it is under the direction of Colonel Barry, a devious yet still compassionate man with many years of experience and service. He is well liked and respected by his men but his position is coveted by others in the Intelligence community.
The three book series takes place of several years but it starts in the late 50's. Though no actual date is mentioned in the book, the facts mentioned reveal the time period. King Idris of Libya is firmly in control, placing it during his monarchy of 1949-1969. The secretary of the Director, a woman much loved by him, had suffered gravely at the hands of the Gestapo during the War and references to the dozen years since the event puts it between 1955 and 1957. This is confirmed by references made to Trelawney's own history.
Regarding the lead character, the first name of Al used by him and those close to him but what it is short for is not mentioned. He is new to the agency at the start of the series but is by no means a young man. He was a young man when he joined the British Navy shortly after the start of WWII and chose to work in the submarine field. A clear head and a keen intellect saw rapid promotion, added by the fact that many senior people died in combat and the field was always opening up. Before hostilities ended, he was a captain of his own boat.
Trelawney might have stayed in the navy except for his shart tongue and his total unwillingness to back down when he knew he was right. Even when he saw that vested interests by the other side would keep them from admitting he was right when he was right, he still hung on. This lack of professional sense kept him from the promotions his actions merited and he was "allowed" to resign.
This staunch pigheadedness continued in the nearly ten years afterwards. Three different careers came and eventually went as he found it impossible to keep his mouth shut when it was prudent to do so. Now needing a new job, he decided to try the Intelligence community and approached them for a job. Since it was usually the other way around and Trelawney was quite a bit older than normal, he was rebuffed. He tried again and again and then appealed to an uncle for a friendly word. That got him a chance and he made the most of it.
As the series begins, Trelawney has just completed 14 months of training, culminating in an assignment to procure a briefcase from a possible double agent. When the Director, during their first ever meeting, asked if it had truly been necessary to kill the other agent, Trelawney replied, "You wanted this briefcase I was sent to collect. So, it transpired, did he. A conflict of interest had arisen. I resolved it in your favor."
That sums up Trelawney quite well.
Well, except perhaps to add that the "Al" in Trelawney's name is not short for Albert or Allan or even Algernon, but for Alaric. Rather unique.
The series is most definitely centered around Trelawney but the other characters are far more important than in many series. The Director, Colonel Barry, is intriguing to watch. His secretary has her own story and plays a major role throughout. The Deputy Director, Rafferty, is free-speaking, highly intelligent man that Trelawney first respects and then grows to like. And Jane Trask, the lovely agent that Trelawney works against then with is terrific to watch in action.