The common theme of the stories in this volume is that someone dies in a way that seems to indicate a supernatural cause. Everyone jumps to the supernatural conclusion...except Father Brown. Now, Father Brown, being a Roman Catholic priest, does fervently believe in some things we might consider supernatural. But he's not much taken in by superstition, and generally looks for a practical answer to the conundrum of the moment.
I think I liked this series of stories better than I liked the second series, but I can no longer be sure because it was 7 years ago that I read, and declared myself to be unimpressed by, those stories. These were ok, but I find short stories difficult to read. Basically, if one can't read them in one sitting, it's way too easy to lose the thread. Novels are much easier to grasp because one naturally lives with them for several days, and also because a single chapter or two is much easier to finish in a single sitting than is a short story such as one of these. Perhaps it's my age, or the fact that I read at only half the speed for success in college, but I'm heading back to a nice juicy novel.