Gregory Keen is an agent with MI-5.
With the imposing name of Gregory George Athelston Keen, the hero of this three-book series is a serious, determined former Major in the British Army, now an experienced agent in Special Service of Home Security, or MI-5 as it is more commonly known. He has been doing so for several years prior to the first recorded adventure, long enough to have established a good reputation and a confidence in his own abilities. The particular department in MI-5 for which he works is known to one and all as "Crossbow".
Little of his background is mentioned, other than his being around 34 years of age, although in passing it is obvious that he had served in Military Intelligence during WWII. Somewhere along the way he gained ability in a couple of different languages and is an expert in Russian. He is single with a good eye for the ladies but not one to let a pretty leg sway him from his task.
One female with a practiced eye for men noted that he had an odd, disturbing brown face with smooth skin unblemished except for faint lines at his eyes. He possesses a wide forehead with high cheekbones. Slender in build and not particularly tall he gains attention not through his appearance but through his demeanor. One thing that both seems to enhance and detract from people's take on him is his partiality to sweaters and tweed jackets. Clearly he is not particularly worried about what others think of him.
Based on his activities, Keen is a very good detective in addition to being a trained agent. His methodical process of studying the evidence and coming to the correct conclusion is demonstrated clearly. Backing him up on his missions is the junior but still dependable Agent Coutts with whom Keen has a good relationship. Keen knows Coutts quite well and considers him his right-hand man. When Coutts is not able to back him up, Keen is not so much concerned as just annoyed. Coutts is Keen's sounding board and in that regard is irreplaceable. Coutts' proficiency with a knife is another reason Keen values him.
But Keen does not have to backed up. He can take care of himself quite well if need be and the need does arise on several occasions. Still, Keen would prefer to use his brain instead of brawn and as the people he goes up against find out, his brain is especially good.