By now, there are devices that can be identified as newish tropes in Ellery Queen’s stories. This one has two: there is a secret society involved, and there are three suspects, and Ellery has to determine which one is not all he represents himself to be.
The more interesting part of the story is when Ellery describes to his father why one of the three must be the culprit. Then comes the more mundane explanation of which one of the three it is. Of course, the actual identity doesn’t matter, since all three culprits, in this very short story, are barely fleshed out.
But still, it is a very well-written piece of fluff. The cousins had done better, and obviously they were not wasting their efforts on their largest audience. This Week (January 7, 1951) had and estimated circulation of 14 million.
Reading Ellery Queen 
This story was in a collection of game themed mysteries. It was either the last or next last story. There are two ways to guess the con man’s identity. First the way Ellery did it,which I missed but secondly another less subtle reason. For spoiler reasons I will not mention either.