While interrogating a former teacher from Saint Loup, Céleste discovers a new suspect who could be linked to the murder of her father. A victim of prejudice, Arsène is about to lose a major contract. Rose learns very good news and is looking forward to writing to Charles to announce.

Celeste finally discovers who her father's murderer is and puts in place a bold plan to trap him on New Year's Eve. At the same time, Rose breaks into the Countess Castle to save Gustave, risking everything in a clandestine operation. Arsène, meanwhile, is looking for a solution to live his forbidden love story.