A companion collection spanning Rick Riordan's Percy Jackson and Heroes of Olympus worlds, gathering four short stories together with character interviews, illustrations, puzzles, and a quiz. It is not a main-series novel but a grab-bag of extras for fans of the Camp Half-Blood books. The collection opens with "The Diary of Luke Castellan," set years before The Lightning Thief and narrated by Luke, in which he and Thalia follow the goat Amaltheia to an abandoned mansion and are trapped by its monstrous, living interior. "Percy Jackson and the Staff of Hermes" follows Percy and Annabeth as the messenger god recruits them to recover his stolen staff. "Leo Valdez and the Quest for Buford" sends Leo, Piper, and Jason chasing an escaped, runaway piece of enchanted furniture in a comic Heroes of Olympus adventure. The fourth story, "Son of Magic," was written by Riordan's then-teenage son Haley and follows Alabaster C. Torrington, a son of Hecate who sided with Kronos, in a tale weighing the line between life and death. Between the stories the book offers behind-the-scenes interviews, art, and trivia. Because the stories reach across both series and fill gaps in their timelines, The Demigod Diaries rewards readers already familiar with Riordan's demigod world rather than newcomers.