I just finished
The Osterman Weekend by Robert Ludlum. I was re-reading Fleming and going through some of the continuation Bond novels I hadn't read before in preparation for a certain film that will come out in November

and decided--golly, I was just in the mood for another spy thriller. Having never read Ludlum before, I picked
Osterman because it was one of his big early success, was adapted by Sam Peckinpah as his last film, and is substantially shorter than many of his other works. Good stuff, nice paranoia and tension. Ultimately far-fetched in the extreme, but the writing has enough conviction to get you past that. I find Ludlum has a brisk and readable style that doesn't draw too much attention to itself. I might read more Ludlum in the future, but I think the next classic thriller I'll read is Follet's
Eye of the Needle or Ambler's
Journey into Fear.