The film is set at the end of the 1930s on a barren, rocky island in the Åland archipelago, whose only residents are lighthouse keeper Majakkamestari Hasselbond and his family. Hasselbond runs a tight ship and expects his family to conform to his regime. The 13-year-old orphan Karl is sent out as a new assistant, but Hasselbond would rather have his son Gustaf do the job and rejects Karl. In fear of being sent away, Karl makes himself useful wherever he can. Gustaf is initially happy to have someone his own age on the island; Karl helps with the math lessons that the elder Hasselbond regularly uses to humiliate his son. But things change as the father becomes increasingly impressed with Karl and starts showing him preferential treatment, even using him to further disparage his submissive son. The interplay of tyranny, obedience and subjugation grows increasing intense. Only when Karl reveals a well-guarded family secret do the oppressed begin to revolt.