The Demigod Diaries is a companion book for The Heroes of Olympus, much like how The Demigod Files was for Percy Jackson and the Olympians. Within it are three Short Stories: The Diary Of Luke Castellan, Percy Jackson And The Staff Of Hermes and Leo Valdez And The Quest For Buford, all from the POVs from the short stories' Title Character. There's also a story written by Haley Riordan, the Son Of Magic. Along with these stories is a letter from the Senior Scribe of Camp Half-Blood, a interview with George and Martha (Hermes's snakes), maps of both Hal's House and Bunker 9, games and various pictures including some official pictures of some characters.
The short story The Diary Of Luke Castellan is a passage from Halcyon Green's diary; though the passage is written by Luke as the title implies. The story reveals a moment of Luke's earlier days back when he was traveling with Thalia before they got to Camp Half-Blood. The story begins with Luke and Thalia following the goat Amaltheia; one of Zeus's sacred animals, due to Thalia believing that she's a sign from her father, Zeus. This led them into discovering, entering and being trapped within Hal's mansion with several leucrota.
The short story Percy Jackson And The Staff Of Hermes begins with Percy and Annabeth relaxing together in Central Park. Annabeth reminds Percy that it's their one month anniversary with Percy failing to take her out for a special dinner, like he promised. Luckily for Percy they're interrupted by the god Hermes. Hermes's then quickly enlists their help in retrieving his staff; the caduceus, which was stolen by the giant Cacus.
The short story Leo Valdez And The Quest For Buford takes place between The Lost Hero and The Son of Neptune. In it Leo is forced to seek the help of his friends Jason and Piper in finding the table Buford when he runs away after being polished with Windex. The reason this is so important is because Buford has within his drawers the device he needs to complete the Argo II's engine. To make things more difficult though the three have only one hour to do to ring Buford and get the device he's carrying into the Argo II's engine or else it will explode destroying Bunker 9, most of the woods of Camp Half-Blood with a 35% of more being destroyed. It also doesn't help that some Maenads are in the woods looking for Dionysus.
The short story the Son Of Magic is about the demigod son of Hecate, Alabaster Torrington. It's revealed that Alabaster is one of the demigods that fought for Kronos and remained a enemy of the Olympians even after peace was made, though they ignore him due to a deal they made with Hecate. The story is about Alabaster trying to kill his half sister, the monster Lamia, who's been attacking for several months and will not stay dead. The story is told by the POV of Dr. Claymore, a mortal ally of Alabaster.
Provides Examples Of:
- Cards of Power: Alabaster's Mistforms seem to be held within cards.
- Character Name and the Noun Phrase: Three of the short stories are this, The Diary Of Luke Castellan, Percy Jackson And The Staff Of Hermes and Leo Valdez And The Quest For Buford
- Creator Cameo: The Senior Scribe of Camp Half-Blood is Rick Riordan who even got his son Haley to help him gain the secrets of Alabaster Torrington.
- Dramatic Irony: Like May Castellan before him, Halcyon Green looks into Luke's future and sees his tragic fate. Though he does his best to help by warning Thalia and giving Luke the diary so he can reflect on his decisions, he is ultimately unable to stop fate.
- Drunk on Milk: The Maenads are getting drunk off of eggnog since they can't have wine yet.
- Foreshadowing: When Hal reads Thalia's future, he promises her that "[she] will find [her] family again." Thalia insists that she would never return to her mother, and Hal gently tells her that that isn't what he meant.
- Magic Staff: Hermes's caduceus and it's revealed that it has a "laser mode".
- Mix-and-Match Critters: The leucrota have a lion's body with rust-red fur, hooves like a horse, a whip-like tail and a head that looks like a cross between a horse, wolf and human.
- Muggles: The mortals of course, though Dr. Claymore is the one that stands out.
- Nature Spirit: The Maenads are stated to be a kind of nymphs.
- Our Giants Are Bigger: Cacus, though he's stated to be actually rather small for a giant, being about 10 feet tall.
- Our Monsters Are Different: Cacus, the leucrota and Lamia.
- The Promise: We get to see Luke's perspective on his first meeting with Annabeth, when he gives her the knife that will eventually kill him.
- I swallowed the lump out of my throat. Annabeth was so young, but she'd learned a hard lesson, just like Thalia and I had. Our parents had failed us. The gods were harsh and cruel and aloof. Demigods had only each other. I put my hand on Annabeth's shoulder. "You're part of our family now. And I promise I'm not going to fail you like our families did us. Deal?"
- Screw Destiny: Thalia's reaction to Hal's prophecy about Luke. She's furious with him, and refuses to even consider the possibility of Luke betraying someone.
- "A betrayal," Thalia said. Her tone was dangerous, "You mean someone betrays Luke? Because Luke would never betray anyone."
- Short Story: This book contains four stories The Diary Of Luke Castellan, Percy Jackson And The Staff Of Hermes, Leo Valdez And The Quest For Buford and the Son Of Magic.
- Villain Episode: A Start of Darkness variant in the form of The Diary Of Luke Castellan, which focuses on the main villain of Percy Jackson and the Olympians from his POV.
- Voice Changeling: The leucrota are stated to imitate human voices.
"What you learn from their experiences could very well save your life!"
