"Castle Gripsholm" is a satirical novel that tells the story of a couple's holiday in Sweden. The narrator and his girlfriend Lydia, also known as the Princess, decide to spend their summer vacation at a castle named Gripsholm. Their idyllic vacation is interrupted when they discover a child being mistreated at a nearby sanatorium, leading to a critique of authoritarianism. The book is filled with humor, wit and a deep love for humanity, while also offering a scathing critique of society's ills.