"The House in the Cerulean Sea" is a fantasy novel by TJ Klune that follows the story of Linus Baker, a caseworker for a government agency that oversees magical children. Linus is assigned to investigate a mysterious orphanage run by Arthur Parnassus, where he meets a group of extraordinary children, including a gloomy sprite and a giant. As Linus spends time at the orphanage, he discovers the importance of love, acceptance, and the value of family. The story explores themes of prejudice and belonging, ultimately leading Linus to question the rigid rules of his society and his own beliefs.