Undine is a young woman with a degree in urban history who gives guided tours about the development of Berlin. She works freelance and lives in a small, impersonal flat. As ordinary as her city life may seem, her secret weighs heavily. When she is left by her boyfriend for another woman, she is caught up in a curse that would mean death for one person and a farewell to earthly existence for another. But Undine resists her destiny. At the moment of betrayal, Christoph appears and she falls in love with him. He is an industrial diver and shows her his underwater world - which she already knows. And which is part of her secret and the curse she can't seem to escape. Undine is young, but has an old, mythical name. In the myth, she lives in a forest lake, a beautiful, virginal nymph. A man who steps onto the shore of the lake and calls her name becomes her wife. If the man betrays love, he must die - Undine will kill him. The Undine in the film is light and clever and stubborn.