Percy Jackson: The Demigod Files
Rick Riordan
Puffin

In these top-secret files, Camp Half-Blood's senior scribe, gives you an inside look at the world of demigods that NO regular human child is allowed to see. If you’re armed with this book, you’ll have everything you need to know to keep you alive in your training. Essential reading for all young demigods!

Also in the same series:
Percy Jackson and the Lightning Thief
Percy Jackson and the Sea of Monsters
Percy Jackson and the Titan’s Curse
Percy Jackson and the Battle of the Labyrinth
Percy Jackson and the Last Olympian