In anticipation of the Oct. 2 release of Rick Riordan's new fantasy novel "Mark of Athena," Google Books has released several of the book's chapters for preview online.

Click here for the free preview of "Mark of Athena" on Google Books 

The third novel in Riordan's "The Heroes of Olympus" series, "Mark of Athena" is told from the perspectives of four different demigods, including Annabeth from "Percy Jackson & the Olympians." The book unites the Greek and Roman main characters from the first two novels in the "Heroes of Olympus" series -- "The Lost Hero" and "The Son of Neptune."

"Mark of Athena" finds seven demigods journeying by air across the United States and by sea to Rome on their quest to defeat the earth mother, Gaea, in a fantastical ship called the Argo II. Meanwhile, war is breaking out between the Roman and Greek demigods they left behind, and only Annabeth, the daughter of Athena, can restore peace.

"The Greek and Roman demigods are at odds, and danger is brewing," said Suzanne Murphy, vice president and publisher, Disney Publishing Worldwide. "This fall, Rick Riordan's millions of fans will be asked 'Whose camp are you in?' and can profess their loyalty by joining the Greek camp (Camp Half-Blood) or the Roman camp (Camp Jupiter)."

"The Heroes of Olympus" is a five part series of books that will end in 2014. The series chronicles the events of seven demigods and their obstacles involving the waking of the earth goddess, Gaea, and their efforts to stop her. It picks up a few months after the end of "Percy Jackson & the Olympians" series.

Riordan is largely known for his hugely-successful young-adult series "Percy Jackson and the Olympians," and the "Kane Chronicles." "The Lightning Thief," the first book in the "Percy Jackson" series, was developed into a feature film. He is also the author of the multi-award-winning "Tres Navarre" mystery series for adults.

With a little prodding from his students and his own children, Riordan made the transition from being a school teacher who moonlighted as a novelist into a full-fledged author.

"I was a middle-school teacher for many years. My students knew me as a storyteller. I would do mythology tales in the class and they would always say, 'Mr. Riordan, you should be a writer.' I would always put them off and say, 'No, no, I already write for adults,'" said Riordan to Entertainment Weekly.

"It took me a while to figure out my students were right. It really is the audience I know best. What really triggered it for me was when my older son Haley was having trouble in school. 'The Percy Jackson' story was something I told him as a bedtime story. That's where the series came from."

Writing for children isn't as easy as you might assume, though. Riordan divulges that writing to a younger age group is actually far more challenging in many ways than writing for adults. "Kids, if anything, are harder to write for [than adults] because they are a more discerning audience," says Riordan.

"They will not stay with you if you go off on a tangent or if you give them extraneous information that doesn't serve the story. You really have to tell a tight story. You have to give them humor and suspense and believable characters. All those things that adults want too, but you have to be really on your game when you're writing for kids."

In 2010 Riordan launched two bran new series that both debuted in the number one slot on multiple best-seller lists: "The Kane Chronicles" and "The Heroes of Olympus".

In 2011, Riordan received the Children's Choice Book Award for Author of the Year.

"The scope of the book is huge," says Riordan. "My biggest challenge is to take all the different strands, all the things I've set up, and merge them into one huge stage. That was the biggest challenge, but I have to say it was also the biggest treat. Some of the relationships that came out of the book, I was not at all expecting. I just hadn't really considered all the different permutations. I'm really pleased with how it came out."