Gwenn is a young woman from Lann Vraz, a wild Breton peninsula where oyster beds and a nature reserve coexist. After being away from her family in South America for five years, Gwenn decides to return to her family with the hope of finding Mark, her childhood sweetheart. He now lives with Aurélie and has since taken over the management of the nature reserve. Gwenn returns in the midst of a conflict between the nature reserve's ecologists and her family's oyster farmers, following a plan to establish a new oyster bed for triploid oysters on the edge of the reserve.

Mael is fifteen when he meets Kevin, a childhood friend of his mother's, who has recently returned to Brest. But this encounter upsets Liza, who blames Kevin for the death of her twin brother, Lomig, at twenty. To protect her son, she will have to confront a past she has erased from her memory.