The Break in the Line attracted me because it is one of the Fontanas with the same look to the Desmond Bagley's I first saw as a kid. I particularly like the use of the green in the cover title. Berkely Mather had a whole series and I guess was a well-enough respected military espionage writer that his name got to be much bigger than the title.
The story takes place in cold war southeast Asia. The protagonist, cynical and self-effacing, screws up what was supposed to be a pick-up mission upriver into Burma. He sort of hopes he'll get fired and can get out of the game altogether. Instead, his superiors corner him into taking a more risky job (both personally and professionally) of following a double agent from Calcutta far to the north, across the Himalayas (dangerous) and into China (super dangerous) in the hope of finding "the break", the point where the Chinese were meeting with their agents.
It was a gripping story, especially when they get into the mountains. Both the espionage stuff and the outdoor adventures stuff was good. The former had lots of tense stops at small mountain villages where they had to try and not stand out too much (or be hidden entirely by allies). There is a cool part in Tibet where the monks are basically fascist thugs, no friends to the Chinese (though possibly with informers among them), but very scary to anyone else. My only complaint was that the protagonist had that tendency to be a dick to everybody as well as constantly down on himself. You see this in these British books of the 60s and 70s and I've never quite understood the appeal. It makes them not likable at all, which I guess was part of the point. Ultimately, the portrayal of the political reality of his situation makes it quite believable that he would be a stressed-out dick, so at least it wasn't forced.
Another funny thing happened when I was reading this. There is a map at the beginning (which I always appreciate), but it's weirdly oriented and badly labelled. It's a section of southeast Asia, centered around the northeast corner of the Bay of Bengal. What was driving me nuts was that it showed Pakistan to be south of Bhutan and east of India! I couldn't believe that they could have made a mistake so I finally started looking into it and it turned out that there used to be two Pakistan. Rather, Pakistan was divided into two after Indian independence, I guess because there were Muslim communities on either side of India. Eastern Pakistan felt neglected by their more powerful western counterpart and eventually there was a war of independence and eastern Pakistan became Bangladesh in 1971. The Break in the Line was published in 1970. Kind of cool that it caught that little geo-political window in history where Bangladesh was part of Pakistan.