Well, read it straight away, of course!
Here's the punch line. Percy has DISAPPEARED and the whole of Camp Half-Blood is in a state of panic, especially for Annabeth (I mean, would you want to have a brand-new boyfriend and then have him suddenly disappear on you?).
In this brand new series featuring the old and well-loved world of Percy Jackson, we are introduced to new characters: Jason, son of Jupiter (yep, you heard me. ROMAN, not Greek, except he doesn't know that yet) Piper, daughter of Aphrodite (except she's not stuck-up, thank the gods) and Leo, son of Hephaestus. Jason has lost all his memory except for his name.
So Jason and Piper and Leo arrive at Camp Half-Blood and are almost immediately sent on a quest. They face everything from evil enchantresses, to metal angels, to snow goddesses, to hungry wolves and so on.
I LOVED the Percy Jackson series, so of course, as soon as I found out about this book, I was so excited, especially since I knew I was going to see old friends. But then I found out he wasn't there... But then that just made me really excited to read the next book. If Percy wasn't there, I would probably have screamed something along the lines of: "Where is Percy? He's supposed to be the hero of this series!!!" Sorry Jason, but you will never live up to Percy's legacy.
I COMPLETELY and UTTERLY recommend this book, especially if you loved the Percy Jackson series.