Jason has amnesia. He wakes up on a school bus on the way to the Grand Canyon with what appears to be his very confused girlfriend (Piper) and a bemused, slightly disbelieving best friend (Leo) who both seem very surprised that he can't remember spending the last few months together at the "Wilderness School", a boarding school for juvenile delinquents. Not that the field trip to the Canyon makes things better. One of the other school kids sprouts wings, and tries to kill Jason and his friends. The coach turns out to be some sort of half-goat-man and to top it all off, Jason appears to be able to fly, as he discovers when he has to hurtle down into the Grand Canyon to save, Piper, his supposed girlfriend.
By the end of their VERY eventful day, Piper, Leo and Jason find themselves in upstate New York at Camp Half-Blood being told that they are demi-gods and the reason that Piper and Leo can remember a whole semester with Jason is because the magical mist that clouds the minds of mere mortals from the existence of the supernatural basically rewrote their memories when Jason appeared out of nowhere. In short order, Leo Valdez, whose been an orphan since his mother died in a mysterious fire in her mechanical workshop, discovers that he's a son of Hephaestus, the Greek god of fire, whilst Piper McLean, a tomboy if ever there was one, discover that her long lost mother is Aphrodite, Greek goddess of love, and that the cabin she belongs seems to consist mainly of Barbie and Ken-doll-alikes. Jason's parentage takes longer to be revealed, but a lot of people get very flustered by his arrival at Camp Half-Blood and this is clearly connected with his sudden amnesia.
Camp Half-Blood's most famous demi-god, Percy Jackson, is missing without a trace, and his girlfriend Annabeth is not happy. When there is a prophecy revealing that Hera, wife to Zeus and queen of the Greek pantheon has been kidnapped and that she needs to be rescued before the Winter Solstice or all hell will pretty much break loose (someone is opening the doors to Tartarus, the Greek underworld), it seems impossible that the two events are not connected and that Jason's amnesia and sudden appearance on the school bus with Piper and Leo is not coincidental either. Piper and Leo get called to go on the quest with Jason, whose father is revealed to be none other than Zeus himself.
Leo realises from a vision of Hera that she's been appearing to him since he was a child, and that his half-blood heritage is the reason his mother died. Piper goes along on the quest, even though she believes herself doomed to betray her friends, as she's keeping a secret from them. Her father, a famous movie star, has been kidnapped as well, and is being held hostage. If Piper doesn't trick Leo and Jason to their deaths, her father will be killed instead.
While Jason's friendship with Piper and Leo may have been a mist-conjured illusion, as they fight a number of mythological challenges on their way to complete their quest, they learn to trust each other and work as a team very fast indeed. Will they manage to save Hera before it's too late? Will Jason recover his memories and figure out why to him it seems more appropriate to refer to the gods by their Roman names?
Oh Rick Riordan, not content with one series of books where you utilise absolutely everything relating to Greek myth, followed by one where you do the same with the Egyptian pantheon, now apparently you're introducing the Roman pantheon, while deviously explaining why it's close to, but not quite the same as the Greek. There's a formula here, and it may not work for everyone, but I find that it does for me. More like the Kane Chronicles with the alternating POVs than Percy Jackson's first person narration, this book switches between Jason, Piper and Leo, usually giving them a couple of chapters in a row before switching to one of the others. It allows us to get to know all three characters better.
Because of his amnesia, Jason is absolutely the character that's the hardest to get a handle on. We don't really know who he is, any more than he does. He's clearly had rigorous training his entire life though, and seems very skilled with a number of weapons. Being the son of Zeus, or Jupiter, he seems to have the ability both to fly and call down lightning. This comes in handy when fighting vengeful mythological giants determined to incite some sort of massive-scale conflict with the Greek pantheon. It becomes clear that his amnesia is caused by Hera stealing his memories and she claims to have a very good reason for it. He's also most likely grown up in a place not dissimilar to Camp Half-Blood, if a lot harsher on its recruits.
Piper McLean was at the Wilderness School because she asked a car dealer for a BMW and he agreed. She's always had the power to get people to give her things and persuade them into doing what she wants, and discovers at Camp Half-Blood that this is called "charm speaking", a gift from her mother. Unfortunately, once the people who've given stuff away wake up from their compulsion and contact the police, Piper would end up in trouble. Piper has Native American heritage on her dad's side, although her father seems to try to distance himself completely from it. She desperately wants to be home schooled, so she can spend time with her famous dad, but he mostly seems far too busy for her. Nonetheless, she's desperate to save him, even though doing so may put her friends in terrible danger instead.
Leo Valdez was diagnosed with ADHD at an early age and has always had a knack for fixing things. Fiddling and constructing things when he's nervous, even before he discovered that he was a demi-god, he knew he wasn't like other kids. Jason not only appears to be completely fire-proof (the clothes he wears as well, conveniently), but can actually summon fire if he concentrates. Hera, who he thinks of as a sort of demented grandma, kept appearing to him as he was growing up, making portentous comments about his future, but he always just thought she was a nut. Now he discovers that not only is he the son of a god, but that there's clearly some sort of grand destiny in store for him.
The first book in a series of five, it's clear that these books are going to reunite readers with some of their favourite demi-gods from the Percy Jackson books (because I have no doubt that while he's missing in this book, he'll turn up before too long), while introducing a bunch of new demi-god teens to root for, some of whom appear to have parents from the Roman pantheon as well. It seems that the Roman gods are more warlike, serious and business-like than their raucous Greek aspects. I like a good YA adventure, and will probably blaze through the rest of these over the summer.