“An intriguing and immensely enjoyable novel with a clever locked room puzzle. Highly recommended”
https://www.goodreads.com/review/show/3938242660
Also, in an unpublished review, due to an ISBN snafu, Publishers Weekly writes:
“Impossible murder novels don’t get much more ingenious than this one… Fans of subtle fair play will be enthralled by this golden age classic.”
I couldn’t agree more.