The Son of Neptune is the second book in Rick Riordan's Heroes of Olympus series and marks the return of Percy Jackson. While his whereabouts had become clear to readers towards the end of The Lost Hero, Percy himself has little idea where he has been and what he might have done to earn the hatred of the Gorgon sisters. Although Percy's inconvenient amnesia means that he doesn't remember killing Medusa, her sisters certainly do and so they have been pursuing him with a vengeance (and a tray of sample snacks) across the country for months. Fortunately for Percy, the pursuit ends just outside of Camp Jupiter, the Roman equivalent of Camp Half-Blood. 
 After being ambiguously advised by Juno, Percy decides that he will head for the relative safety of Camp Jupiter and, along with Hazel Levesque and Frank Zhang, two demigods who happened to be on guard duty outside the Camp, he manages to defeat the Gorgons. Although Reyna, the Praetor of the Camp, is initially distrustful of Percy, she allows him to join the legion on a probationary basis and assigns him to the Fifth Cohort. It soon becomes clear that life amongst the Romans is just as complicated and dangerous as life with the Greeks and so Percy doesn't get to enjoy his safe haven for long. After the Fifth Cohort win the Camp's war games, Mars appears and orders that Percy, Frank and Hazel embark on a quest to the North to free the imprisoned Thanatos and so restore order to the underworld. 
 The Son of Neptune is another excellent adventure story from Rick Riordan. While Jason Grace is a great hero, Percy Jackson is even better and so it is wonderful to be able to follow his adventures once again. The quest to free Thanatos involves lots of thrills and spills and so this story contains all the excitement that fans of Percy's previous outings will expect. As well as the action there is also plenty of humour, wit and the occasional dire pun. The story and the characters of The Son of Neptune result in a fascinating mix of Greek and Roman mythology as the fantastical worlds of the various demigods collide.