Epitaph For A Spy by Eric Ambler is a jolly enjoyable read!
Written and set in the 1930s, the first half seems a bit like an Agatha Christie whodunit (not that I’ve read one!). Guests at a hotel, a stolen item, our hero trying to determine who’s the thief etc.
Although continuing in the same vein, somehow it becomes a lot more interesting. It’s very well written and somewhat old-fashioned, but I really liked it. A nice read and recommended.