Claire Cousteau is one of France's most esteemed biologists, with a seemingly perfect family life, but she has become increasingly frustrated by her marriage and her husband's affairs. As the Cousteaus prepare for a summer in Brittany, Claire's son Nico asks if his new girlfriend, Julie, can join them? Julie has conundrums of her own - she is an ambitious woman, and unsure if Nico really is her match. But what the family don't realise is that Julie and Claire have met before, in a Parisian hotel during a night that Claire thought was her secret. Beneath the Breton sun, could their surprising bond alter the course of their lives for all time?