Sarah (Eva Green) 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 be part of the crew of a year-long space mission called "Proxima", it creates chaos in the mother-daughter relationship.