I can understand why it wasn't a highly acclaimed success when it was published as there's plenty of elements which are very innovative.
It starts as a witty comedy of manners with a witty description of a newly married couple and it becomes a twisty and surprising mystery that kept me guessing till the end.
The book-in-the-book and the final twists are intriguing, the puzzle to be solve if quite tricky and the way it is solved it's very fascinating as it mixes psychology and classic police work.
I find the moral judgements on Sheringham's behaviour I read in some reviews a bit funny: what happens is not unusual for a Golden Age Mystery.
Berkley plays an intellectual game with his readers and I loved the game and the puzzle.
Highly recommended.
Many thanks to the publisher for this arc, all opinions are mine