The following version of this book was used to create the guide: Klune, TJ. The House in the Cerulean Sea. Tom Doherty Associates, 2020.

Klune’s novel is divided into 20 chapters, each told by a third-person limited narrator who focuses on Linus’ thoughts and feelings. The first third of the novel focuses on highlighting how depressing Linus’ life really is. The second third of the novel revolves around Linus’ one-month stay at Marsyas orphanage and the friendships that develop there. The final third highlights the romantic tensions between Linus and Arthur, as well as the growing danger the orphanage faces at being shut down.

To begin, Linus is a caseworker for the Department in Charge of Magical Youth (often referred to by its acronym, DICOMY). He visits orphanages for magical children and makes recommendations on whether or not they should be shut down. Linus never lets himself get emotionally involved in his cases. His dedication and many years of service impress Extremely Upper Management, who entrust him with a top-secret mission. Linus is to spend one month investigating Marsyas Orphanage, led by Master Arthur Parnassus, a supposedly dangerous man. All the children there are extremely powerful and unique. Extremely Upper Management wants to know whether they should let the orphanage keep running or not.

Linus arrives at Marsyas full of prejudices against magical people. Gradually, Arthur and his coworker, Zoe, show him that he has nothing to fear. The children—Talia, Theodore, Lucy, Sal, Phee, and Chauncey—eventually warm up to Linus. Linus finds himself immersed in their playful, magical world. Without intending to, he grows attached to the children and develops feelings for Arthur. The novel’s climax occurs when Linus uncovers Arthur’s secret. Arthur is a phoenix. He grew up at Marsyas Orphanage, abused by its master and afraid of his own power. That is why DICOMY allows him to run the orphanage today. They are frightened he will come forward with allegations against the organization. Arthur benefits from this situation by being able to run the orphanage and help foster a generation of happy, confident magical creatures. DICOMY benefits by being able to keep tabs on Arthur who, after all, is a very powerful phoenix. Linus becomes overwhelmed by all this information and unsure of whether he can even trust Arthur.

When the time comes for Linus to return to his job, the children are devastated. Even Linus is depressed at the thought of it but assures them that he has work to do back in the city. One night, after Linus’ goodbye party, Arthur begs him to stay. Linus resists this temptation and returns to the city the next day. He tells Extremely Upper Management, who are furious with him for developing a bond with the children and Arthur, that they are wrong to treat magical creatures different from human beings. Linus waits three weeks to finally receive confirmation that Marsyas Orphanage can remain open. After that, he returns to Marsyas full of apologies for ever leaving. He and Arthur kiss, at last.

The epilogue describes Linus’ life one year after the final chapter. Linus and Arthur are happy. Zoe still helps at the orphanage, along with her girlfriend, Helen. Extremely Upper Management all resigned after someone leaked information about their discriminatory practices. Linus and Arthur plan to get married and legally adopt all the children as their own.