For whatever reason (intellectual sloth, most likely) I hadn't read the Ashenden stories by W. Somerset Maugham until ratmmjess essentially shamed me into it. Really terrific prose style, winning character, unsentimental but adult examination of responsibility and espionage (taken from his own wartime experience in the secret service), all coupled with an arch and sometimes hilarious observation of humanity -- the only flaw (if you can even call it that) is that Maugham's devotion to seeming naturalism in plot (doubtless a reaction to the general run of 1920s spy fiction) sometimes tugs off course his real gifts for invention and architecture in story.
It took me a ridiculously long time to make sure that Volume 3 of Penguin's Collected Short Stories of Somerset Maugham does, in fact, hold all the Ashenden stories. But it does. Buy or borrow with confidence.