This is a book by Agatha Christie.
I have read many of Ms. Christie's books and liked some better than others. This is one of the better ones!
It was written a long time ago (1922) and was one of her first. The "modern" language (slang) of the book sounds a bit funny at times and at others is a bit hard to comprehend, but this is a very good story.
The basis may seem a little hard to accept today - early Red Terror - but the plot is well done. This was one of the few that I figured out before the "reveal", but I think it may have been just luck.
Lots of twists and turns. Give it a try if you like mysteries.