The Wives by Tarryn Fisher is a psychological thriller in which the protagonist shares her husband with two other wives, having him to herself only on Thursdays. The unsettling premise becomes more unsettling as she becomes obsessed with the idea of learning who these other women really are, and who her husband really is. The plot moves quickly and there’s a sense that the protagonist is losing control. Even though you know the author is manipulating you, you can’t stop turning the pages to find out what’s really going on and how it all will end. Here’s what Kirkus Reviews says:
https://www.kirkusreviews.com/book-reviews/tarryn-fisher/the-wives/