I read Tunis and Time from the collection. I have to be quite honest and say that I didn't like it at all...not one bit. I'm not sure what exactly was "mysterious" about it.
I thought it was just a story about a spy. Then at the very end it gives an italicized paragraph that reveals what happens to the spy AFTER the story...Not much mystery to it.
I chose it, originally, because I thought the main character sounded alot like Sam Spade in Maltese Falcon. He WASN'T!
Sam Spade is a cool character; good looking, smart, macho. In "Tunis", Layton is just an elderly, slovenly, loser who can't make good decisions.
I really don't think there was much mystery to the story. The reader is given alot of info about this guy, and then suddenly it is revealed that he was tricked. But since the big "reveal" happens to occur AFTER the story, there isn't any "aha" or "Wow". It's just sort of, "Oh, okay."