The Chateau (The Original Sinners #9) by Tiffany Reisz

As the Jack-of-All-Wicked-Trades for a secretive French military intelligence agency, 24-year-old Lieutenant Kingsley Boissonneault has done it all—spied, lied, and killed under orders. But his latest assignment is quite out of the ordinary. His commanding officer's nephew has disappeared inside a sex cult, and Kingsley has been tasked with bringing him home to safety.

The Chateau is a new standalone Original Sinners novel from international bestseller Tiffany Reisz, author of The Siren and The Lucky Ones.