Brownian Motion refers to the aimless movement of particles in fluids and gasses, a consequence of collisions between atoms and molecules that are constantly in a state of motion.

Charlotte is a doctor in a laboratory of the Brussels University Hospital. She is married and has a child. In an apartment that she has rented, she has casual sex with some of her patients. These are men who contravene conventional ideals of beauty, because they are old, hairy or extremely fat. Sleeping with them for her is almost like a scientific experiment. When her husband Max finds out about this, it is not only their marriage that is at risk of disintegrating.
The couple turn to therapy. They search for words, for rational explanations. But Charlotte cannot, and does not want to describe her desires in words. Finally, the family makes a new start, in India, where Max works as an architect. Sandra Hüller plays her character, who hides a secret, with great intensity. She is vulnerable yet tough, sensitive yet untouchable.
Nanouk Leopold structures her film in three parts, narrating with a strict formality and confident style. The bustle of Charlotte and Max‘s successful working world and family life is followed by a phase of contemplation in which the couple try to come to terms with their situation. Surrounded by the bright colours and cultural alienation of India, they end up revolving around the capability of each accepting their partner for what they are.