John Smith is a former agent for the British Secret Service.
He worked in that capacity for quite a few years and was, according to his boss, one of the best. Even several enemy agents that he meets agree that at his best, he was extremely good.
Eventually, however, the callousness and brutality of the missions he gets finally weighs too heavily on him and he knows that he has to get out. Knowing also that his boss, a man called Max, would not allow him to leave without incentive, he began to create a dossier on the missions. Using this as blackmail, he gets his release.
Despite the tag of being an anti-hero, Smith is just a man who has had to do too many bad things and wants to be left alone. After so many years of working on his own, he chose poorly the enquiry agency business which he doesn't enjoy and isn't too successful at.
Five years pass prior to the start of the series, time in which Smith gets married and divorced, starts his own private investigator business and sees it coming almost to an end with a lack of clients. Then a job for his ex-wife gets him involved in what seems like a standard divorce case, hers, and suddenly he is inveigled back into the cloak-and-dagger world.
The Max for whom Smith worked when he was an active agent and who forced him back into involuntary service is a particularly nasty piece of work, a man that Smith greatly dislikes and distrusts, with good reason, and the perfect man for the job that he does, a job that is filled with deceit, back-stabbing, lying, and the like. It is Smith who is not so into the work. Luckily, he distrusts everyone enough to believe nothing he is told.