After the death of his son's babysitter, caused by UBH, a synthetic drug that is starting to flood the market, Commissioner Max Vernet convinces his superiors to set up an infiltration, the only way to trace a production and distribution network that is as mysterious as it is dangerous. To do this, he meets Aurélie, a single mother and chemist in the police, and asks her to offer her services as a chemist to the network run from Marseille by the charismatic Jesus on the pretext of being able to improve the product. But Aurélie refuses, her family balance and her son, whom she has been raising alone since the death of her partner fifteen years earlier, matter more than anything.