A young apprentice from a watchmaking school is found dead at the foot of a cliff. The thesis of suicide is privileged: Manon, the only girl in her promotion, would have cracked under the pressure. Jeanne Keller, the principal educational adviser of the establishment does not want to believe it. With the help of her friend Alice, a policeman, Jeanne will lead an investigation which will lead them to the other side of the Swiss border, to the heart of world watchmaking and which will force her to face her past...