It is 1979 and Albertine, 10, and all her family members have gathered in Brittany to celebrate the birthday of her grandmother. Everyone thinks that the Skylab space station from NASA will fall on their heads this summer. The meeting turns into a crazy weekend full of revelations, love and song.

Magali plays in a brass band. Guillaume drives a small tourist train. Both spin a perfect love, they share modest dreams and their baby is about to come. But an unexpected news upsets their routine: a man appears and announces that he is Guillaume's estranged father and also reveals that Guillaume is his legitimate heir of a kingdom offshore of France and England. Guillaume and Magali start to dream of a life as monarchs, surrounded by faithful subjects in their castle, enjoying their wealth. But reality is often different to what you can imagine.