I FINISHED THE RULE OF FOUR last week and thoroughly enjoyed it. I didn't notice any obvious historical errors, but most of the history is outside my areas of expertise. It's a well-paced thriller and coming-of-age story with interesting characters, and the central role of the Hypneratomachia Polyphili is a lot of fun. It was indeed timely, as I'd guessed. The code system seemed a bit contrived, but perhaps they really did have such things in the Renaissance. And I do doubt that a university senior, even from Princeton, could really decode all that abstruse Renaissance Latin and translate it in the time frame allowed.
I'll avoid spoilers, but I'll note, for what it's worth, that the key to the whole puzzle involves the item that most frequently brings readers to PaleoJudaica via the search engines. And the solution of the puzzle is so marvelous that it's heartbreaking it isn't real.
If you enjoy reading PaleoJudaica, chances are you will like The Rule of Four. I recommend it to you.