Undine (Paula Beer) works in Berlin as a historian and guide to the city's development. She has a small apartment at Alexanderplatz, a Master's degree in history, and a freelance contract. When her lover Johannes leaves her, her world collapses. But underneath the appearance of her modern city life lurks an old myth: if the man Undine loves betrays her, she has to kill him and return to the water she once came from.
Undine fights against the curse but thinks she has no choice. Then she meets Christoph (Franz Rogowski), an industrial diver, and falls for him. This is a new, happy and innocent love filled with curiosity and trust. But when Christoph starts to feel that Undine is running away from something, she has to face her curse once and for all. She doesn't want to lose this love.