Summer 1910. Several tourists have vanished while relaxing on the beautiful beaches of the Channel Coast. Infamous inspectors Machin and Malfoy soon gather that the epicenter of these mysterious disappearances must be Slack Bay, a unique site where the Slack river and the sea join only at high tide. There lives a small community of fishermen and other oyster farmers. Among them evolves a curious family, the Bréfort, renowned ferrymen of the Slack Bay, lead by the father nick-named "The Eternal", who rules as best as he can on his prankster bunch of sons, especially the impetuous Ma Loute, aged 18. Towering high above the bay stands the Van Peteghems' mansion. Every summer, this bourgeois family - all degenerate and decadent from inbreeding - stagnates in the villa, not without mingling during their leisure hours of walking, sailing or bathing, with the ordinary local people, Ma Loute and the other Bréforts. Over the course of five days, as starts a peculiar love story between Ma Loute.
Having been fired from her old job as a real estate agent, 40 years old Constance faces severe pecuniary issues : she cannot rent a flat anymore and she doesn't find another job in Paris. With no other option left, she decides to call her former boss, from the small agency in La Rochelle where she started her career : to her surprise, he tells her that he is actually hiring, as the housing market appears to be growing in the area. He explains that he already found someone, but she is convinced she will get the job because of her experience and extensive qualifications. She does not : it is indeed Audrey, a younger and prettier woman, which is hired instead. This is too much for Constance to take.
A violinist looks to inspire his students at a challenging music school.