William's Picks
Heroes of Olympus - The Lost Hero by Rick Riordan
This book is about four demigods from the Percy Jackson series: Annabeth, Piper, Leo and Jason. Leo is a great builder and he makes a mechanical dragon. The demigods use the dragon and face monsters on their way to find Percy Jackson.

This is my second favourite in the series.
Heroes of Olympus - The Son of Neptune by Rick Riordan

This is my favourite book of the series.

Percy Jackson is back: at the start of the book Percy is fighting and running from Medusa's two sisters, the gorgons who never die. Percy has no memory left. He is rescued and brought to the Roman Camp.

Percy then goes on a quest to find the Greek camp and he must fights monsters and a Titan.
Heroes of Olympus - The Mark of Athena by Rick Riordan
The third in the series: there was lots of action in this one. 

Annabelle and Percy are reunited and have to go with Leo, Piper and Jason to fight Gaya, the Goddess of Earth.