The story's plot isn't complicated. A man has disappeared. An insurance investigator is looking into the case because the man carried a large policy, and his family thinks perhaps his much younger wife is to blame for the disappearance. (Here's something MacDonald would probably have avoided later on. The investigator is named Darrigan, the missing man is Davisson, and one of the suspects is Drynfells. Too many "D" names there.)
There are typical MacDonald observations and descriptions, like this one: "Three lean women in bathing suits sat at one tabel, complete with beach bags, tall drinks, and that special porcelainized facial expression of middle forties trying, with monied success, to look like middle thirties." Or this one: "He drove with his eyes steady, his face fashioned into a mask of tough unconcern. Each time, you bled a little. And each time the hard flutter of excitement ended in this sourness. Murder for money. It was seldom anything else. It was seldom particularly clever. It was invariably brutal."
The whole thing revolves around a real estate deal, with emphasis on the way things are changing in Florida, a theme that MacDonald pursued right up until the end of his career. If you're looking for good, tight writing and plotting in a short story, you can do a lot worse than MacDonald. There are several collections you can find easily enough, including The Good Old Stuff and More Good Old Stuff. Check 'em out.