Two great bloggers agree:
“A tremendously enjoyable detective novel with a first class locked room conundrum”
http://moonlight-detective.blogspot.com/2021/07/the-forbidden-house-1932-by-michel.html
“Another brilliantly creative and wildly entertaining Gallic mystery”
#812: The Forbidden House (1932) by Michel Herbert & Eugene Wyl [trans. John Pugmire 2021]