I loved Steam Trains as a Child

There is another world inhabited by creatures that pretend to be human, but are so debased as to be devoid of any similarity to the humans that exist in the real world. This alternate world is where terrorists and those that hunt them roam. The hunted and the hunters sometimes exchange places, and the idiom "one man's terrorist is another man's freedom fighter," is the order of the day. David Abraham, a world class runner returns from the Munich Olympics after faring poorly in his event, and is now faced with a decision that would alter the course of his life. As a uniformed police officer in London, he has the opportunity to join the ultra-secret department at the New Scotland Yard known only as "The Group." He is interviewed and accepted into this shadowy group, and from there his adventures begin. He is given the mission of infiltrating a well-known terrorist cell in Augsburg Germany, and ends up stumbling on a possible terrorist plot that involves the Montreal Olympics in 1976. His journey takes him into the world inhabited by cockroaches and vermin who don't deserve to live, and along the way he uses some of their tactics to trap and kill them. He becomes a liability to Scotland Yard and his handlers and they try to rein him in, but he uses all his guile to outwit them, with the help of some Mossad agents. The end is unexpected, and leaves the reader breathless, to only crash and burn with David Abraham.