A police inspector tracks a notorious jewel thief, 'Diamond-Lasse,' to a hotel filled with eccentrics.
The Swedenhielms is an old aristocratic family. The head of the family is professor Rolf Swedenhielm. His three children Bo, Julia and Rolf Jr also live in the house. They also have an excellent house maid, Boman. Because of the family's extravagance, they are heading for bankruptcy. But perhaps their problems would be solved if Rolf was awarded the Nobel Prize?
A travelling theater-company performs Offenbach's "The Beautiful Helene" when an officer in the audience notices the similarity in appearance between the leading actor Leonard Pettersson and the king Charles XV. With Pettersson dressed as the king and the other actors as the royal suite, they all go to Herrsunda castle where the officer is trying to make an impression on his fiance.
