Apparently, writing a good whodunit is a lot harder to do than it looks.
I just finished "Forget Me Not", by John Hemmings.
A clear list of suspects. Skullduggery in the background. Several people had motive, means, and opportunity...….and one of them did it.
This one had an interesting twist. When the detective found the clue that made clear who the murderer was, it wasn't anything that had even been mentioned earlier. There was no place where the detective could say, "You see, Gloria always ate Swiss cheese, so that box of Kraft Singles that was mentioned in chapter 3 could not have come from her." None of that tired old, "I didn't realize why that was important" feeling for the reader at the time of the reveal, because the important clue had not yet been shared with the reader.
Nope. The book described a list of suspects, and their motives, and each of them could have put the arsenic in the food, and then the detective saw something and said, "Aha!", but the author didn't let us in on the clue that solved the case until after the murderer was revealed.
For my purposes, which is adapting a cheap novel into a murder mystery dinner, it did have a few interesting elements that could be used. Clandestine relationships and that sort of thing, but in terms of actual puzzle solving, there really wasn't anything. At the point of the reveal, all the information that was available to the reader would have left at least five viable suspects, with no way to distinguish which one actually did it.