The first 90% of this book, set in 1946, was a first rate golden age mystery: an impossible murder in a sealed room, a group of suspects gathered in one house for the duration of the investigation, a diagram holding a key to the solution, and a detective in the classic mold. Up until the denouement I thought this was going to rate 5 stars. But then it all fell apart. Not only was the solution pretty confusing, but the author shows remarkable insensitivity (even for 1946) by using a terrible homophobic reference. So I give it 4 stars for the majority of the writing and plotting, and 1 point for the ending.