Hang on. When I read the first couple of pages, I thought This was set in the 1930s or 40s. But it isn't. This is set in 1974!!
The writing reminds me so much of Above Suspicion, tho, which is set in the 1940s.
So, now that I totally have to adjust my view with respect to context, let's see how MacInnes deals with the aftermath of the Prague Spring and the Cold War setting.