Like every evening, ten-year-old Gaëlle takes care of her little brother Kylian, while their father, Tony, works the night shift. All three of them are surviving in this fragile balance when the social services come knocking at their door.

Sarah is a French astronaut training at the European Space Agency in Cologne. She is the only woman in the arduous program. She lives alone with Stella, her seven year old daughter. Sarah feels guilty that she cannot spend more time with her child. Her love is overpowering, unsettling. When Sarah is chosen to join the crew of a year-long space mission called Proxima, it creates chaos in the mother-daughter relationship.