Businessman Bertrand Deroo is found murdered in a hotel room not in his name, during a 'key party', a form of partner switching. Quspects thus are his wife and the others partaking couples, including hotel manager Marc Verhaegen, whom the victim planned to fire after taking over the hotel group. Van In's team finds several romantic complications, but also stumbles upon surprising shift switches and motives among hotel staff.
—KGF Vissers