February 9, 2023, a month after their return a year back, Juliette, Anna and Cédric have no clue as to the identity of Marc's killer. They rely on the memories they have of the year they're reliving to try to catch the killer in the act. At the same time, Juliette and Karim are looking for solutions to repay their debts. Anna gets dangerously close to Simon. And Cédric will try to save Margot from the accident that had deprived her of her legs.

On the evening of December 31, 2023, Marc, a star surgeon at the Provence hospital, was found murdered at his workplace. As they leave the crime scene, Anna, his ex-wife, Cédric, his best friend, and Lieutenant Juliette Kharoub find themselves stuck in the same elevator. Midnight passes. When the doors open again, Anna, Cédric and Juliette realize that they have been taken back a year, to January 1, 2023.