The House in the Cerulean Sea, Klune's first stand-alone novel published with the Macmillan Tor imprint, was partially inspired by the Sixties Scoop, where the Canadian government removed Indigenous children from their homes and placed them with unrelated white, middle-class families. Seeing the similarities of this event take place in the current-day Southern United States, Klune felt a need to write a story celebrating children's differences and to show the positive effects of giving children a safe and supportive place to be themselves. Linus Baker is a 40-year-old man who lives with his devious cat Calliope, and who works as a case-worker for the Department in Charge of Magical Youth (DICOMY). He spends his work days overseeing the care of magical children in orphanages, and his nights listening to his old records. When Extremely Upper Management calls him, he is given a Classified Level 4 (he had only been given a Classified Level 3 once, which was an unfortunate incident), in what will probably be his most challenging task ever; taking a trip to the Marsyas Orphanage, where six extraordinary children are kept by an equally extraordinary caretaker, Arthur Parnassus.