The young siblings at the Hejrenæs estate, Vibeke and Hans-Henrik, have always gotten along well, so Hans-Henrik decides to celebrate his sister's 21st birthday with a big party at the estate. During the party, the siblings' childhood friend, Ulla, provokes an engagement with Hans-Henrik, and at the same party, Vibeke learns that she is "only" an adopted child. From that day on, Vibeke realizes that she is in love with Hans-Henrik, and suddenly the stage is set for a sharp conflict between Ulla and Vibeke.