Basically, the original location of the Oracle of Delphi (the original Cave of Delphi) was taken back by Apollo's enemy Python while Apollo was being afflicted by his warring Roman and Greek personalities. He later fled to one of his shrines in the Roman lands to have peace between the personalities. While he was there, Gaea told Python to make the Oracle of Delphi tell Apollo a false prophecy, which he told Octavian, which ignited his ego, and inadvertently caused him to make war between Camp Half Blood and Camp Jupiter; this in turn angered Zeus, and Apollo had to stay at the shrine because of it. In the second-to-last chapter of the last book, Zeus claims that Gaea's rebirth, as well as the war in general, could have been prevented if Apollo hadn't let the Oracle of Delphi get taken in the first place. Apollo is then blasted by a lightning bolt by Zeus and disappears. The new series attempts to tell why the Oracle of Delphi was taken, and follows the 'Trials of Apollo' (the name of the series) after he is stripped of his godly state by Zeus and thrown to Earth, with Zeus' final words being 'Your fault, your punishment'. I already read The Trials of Apollo Book One - The Hidden Oracle, and anyone who has read his previous works will LOVE the seemingly new style of storytelling he is attempting to use in this series (the entire book is narrated solely by Apollo, and some of the things he says are downright funny - maybe even funnier than Leo's jokes from the Heroes of Olympus series).
My favorite book is still Lord of the Rings. Hard to beat..
