The Enigma of Room 622 by Joël Dicker

It all starts with an innocuous curiosity: at the Hotel de Verbier, a luxury hotel in the Swiss Alps, there is no Room 622.
This anomaly piques the interest of Joël Dicker, Switzerland's most famous literary star, who flees to the Verbier to recover from a bad breakup, mourn the death of his publisher, and begin his next novel.

Before he knows it, he's coaxed out of his slump by a fellow guest, who quickly uncovers the reason behind Room 622's erasure: an unsolved murder. The attendant circumstances: a love triangle and a power struggle at the heart of Switzerland's largest private bank, a mysterious counter-intelligence unit known only as P-30, and a shadowy émigré with more money than God.

A Russian doll of a mystery crafted with the precision of a Swiss watch, The Enigma of Room 622 is Joël Dicker's most diabolically addictive thriller yet.