Sebastian Kettle is an agent for British Intelligence.
Having been an agent for many years, and a very good one at that, he yearned for the time when he could retire. When he is pushed out by his bosses for being too old and too soft-hearted to make a good spy anymore, their thoughts not his, he suddenly found he missed it. At least he missed the pay he had earned, better than the meagre living he was making on the outside using his engineering skills to repair the odd television or radio.
Then he got a call from his boss with an offer for another chance. Kettle knew that while he probably was too kindly to make a ruthless spy, he was by no means stupid. Something had to be up to get the call to come back and that inevitably meant that his real job would be as a sacrificial lamb. Still, he could use the money.
Kettle is in his late forties at the start of this three-book series. He had been married for too few years to a woman named Myrtle and figures he probably still is as the papers were never signed but that was a while back and he never sees her. He still misses her, though. And thinks of her often. On the few times when he is near other women, she comes back in thought. There is no great angst involved; just a reasonable amount of melancholy.
As he returns to the Service hoping to live long enough to earn a pension, and long enough to enjoy it, he does so knowing that no one really cares what happens to him with the possible exception of his cat, Wilson, and who can say how cats truly feel?
Still, Kettle proves on more than occasion that he may be aged and unappreciated but he is still very good at his craft. He doesn't fight very well and he has no love of guns at all but he is clever, observant, circumspect, and even-keeled. He holds himself in check, neither getting angry nor excited. The fact that others around him do only makes his job that much easier.