The Demigod Files

WHY: Revisiting Riordan's Greek mythological world with my girlfriend before attempting to read the Heroes of Olympus series together.
STORY: This Percy Jackson companion novella includes three short stories, with camper interviews, world-building details and book puzzle games throughout.
The Stolen Chariot adds to the rivalry turned begrudging friendship between Clarisse and Percy as they track the title's namesake from sons of Ares Deimos and Phobos throughout Staten Island Zoo. The Bronze Dragon includes two romantic pairings and is of particular importance to the Heroes of Olympus series, introducing Festus as Beckendorf is trapped in a Myrmekes nest during a Capture the Flag game at camp. The Sword of Hades is definitely the best one, combining every fan's dream of the big three children Thalia, Percy and Nico with a trip into the Underworld featuring angry spirits and the River Lethe.
All three stories are also effective in increasing suspense for the final book in the PJ series, as this is set after the penultimate fourth entry but before The Last Olympian.
WRITING: Classic Rick Riordan humour integrated with just enough detail for a short story format. Whilst there are a few funny bits in the interviews, I found them very skippable (with the exception of Annabeth).
WHO: If you enjoyed the Percy Jackson series you will enjoy this. I'd say it is almost necessary reading if you plan on starting the Heroes of Olympus.