It's one of those hall-of-mirrors British spy stories in which the puzzle is to figure out who is working for whom, and who is double-crossing whom.
I was rereading my Len Deightons, partly to see how much impact they still have post-cold war, and I picked this one up out of order. After the first few pages I remembered that this was third in the Bernard Samson series, set in the 1970's and 80's, but it has close affinities to the Harry Palmer series of the 60's, especially Funeral in Berlin. (This has a 1985 publication date). If you're completely new to Len Deighton I'd start with those, and of course you should read Berlin Game and Mexico Set before this.
Some people think Deighton deteriorated in the later spy books. They contain fewer wisecracks and less descriptive scene- setting. In compensation there's a lot of subtle humor in the portrayal of the Dilbert-like atmosphere of office politics, and the plots are more sharply focussed and draw naturally to a climax. The earlier books tend to jump from episode to episode with a tidying up of plot in the last chapter.