John Morpurgo is an agent with MI-5.
He has served as such for many years prior to the start of this series, accomplishing two things as a result. He has worked his way up the chain by being very good at his work and getting the job done. And he has made an impressive collection of enemies who would like to see him dead and most are not on the opposite side.
There have been many series written in which the main character was a playboy, a skirt-chaser, a Don Juan, and any other manner of description desired but few have actually dealt with a situation in which the character is having an ongoing affair and it plays a major role in the events. At the top of the hate-Morpurgo crowd is the man just below him in the department. The irony is that as the books start, the man despises Morpurgo and doesn't yet know that his wife is having an affair with Morpurgo. The delight that Morpurgo has in dealing with a man who hates him, knowing that he has been sleeping with that man's wife, make this agent even more unlikeable that he already was.
It isn't surprising as the series continues that when Morpurgo just barely completes another mission and makes even more people angry, it becomes clear he is no longer welcome in the agency. A move from being spy-hunter to being spy is forced on him. But now on loan to MI-6, he can't help make more enemies. Morpurgo's way with words and his annoying habit of telling people what he thinks make even would-be friends tire of being around him. Morpurgo is left to ponder what is wrong with all of them even though he knows it is really himself.