Stefan Brand is a rich pianist who likes to go out at night and seduce women. One evening, while returning home, he finds a letter from an unknown sender. The first few lines catch his eye and he spends the whole night reading it. As he goes along, he discovers a past under the passionate gaze of a person he has ignored. About fifteen years earlier, when he was moving into a new apartment, the neighbor’s daughter fell under his spell. She spied on him, followed him, loved him madly in secret. She met him one day and they spent the night together. For him, it will be only a passing fancy, for her it will be the love of her life.