Paul Dark is an agent with MI-6.
He is one of their most decorated and respected agents, having served with distinction for two decades since the time he, at the prompting of and with the support of his father, another trained operative, joined at the beginning of the Cold War. Now as the 60s are coming to a close, he might have been looking for a way to retire with honor, perhaps even with a knighthood among the possibilities.
Dark is also a highly duplicitous traitor, a man who has served two masters for nearly as long as he has been with the Circus. As events unfold which look to bring his house of lies down on his head, he knows he can flee before his identity is revealed and he might have a chance to get away with. He also knows that victory favors the bold and he has never taken the easy way. Striking at those who are looking for a mole but who do not know it is he, he just might survive. That is the route he takes.
When he was recruited as a young man at the end of the Second World War by his father to help out British Intelligence, he thought it to be a noble cause. As he did the work, though, he began to have his doubts about his father's motives since all they seemed to be doing was killing former Nazis. His doubts became solidified when, badly hurt on an assignment, he met a beautiful nurse named Anna. Her job as really a Soviet spy was to turn him and she nearly succeeded. Her death at the hands of his colleagues, though, closed the deal.
As the trilogy begins, Dark becomes aware that his life as a double agent is nearing an end. A Soviet defector is talking about moles and Dark knows he is one of them. His concern is tempered with irony when the head of the department chooses him to help sniff out the bad guys. He can only continue the charade so long, though, and in the second book he must plan his departure and new life in Russia. The questions he then faces is whether he will be as welcome as he hopes and whether he hopes for a welcome as much as he might.
The third and final book deals with being the one person who can help avert a major nuclear war but with both sides having no reason to trust or listen to him and every reason to want him dead, being the real hero for once in his life is likely going to kill him.