The Last Olympian: Percy Jackson and the Olympians, Book 5 (by Rick Riordan)

In the conclusion to the five-volume Percy Jackson and the Olympians series, Kronos and his vast armies of monsters and minor gods finally launch their assault on Mt. Olympus, which means attacking the island of Manhattan. Because the gods are away dealing with Typhon -- the worst monster of all time, who's escaped from his prison under Mt. St. Helens -- it is left to the vastly overmatched and outnumbered demigods, led by Percy, to protect New York and Olympus.

The series thunders to an epic conclusion in this volume, and it's hard to imagine how it could possibly be more satisfying. Everything is amped up here -- the action and violence, to be sure, but also the friendships and relationships, the ethical dilemmas, the scope, and even the delving into the more arcane corners of Greek mythology. And Percy, the delightfully humorous and self-deprecating teen protagonist, comes charging fully into his own as a true hero, one who's fully in command of his powers but is also caring, concerned about others (including his enemies sometimes), and willing to let others be heroes, too, even at his own expense.

Amidst all the exciting action, with gigantic battles that ravage the United States and shake New York to its foundations, it's Percy's growth -- both heroically and personally and echoed by growth in many of the other characters (even the gods) -- that makes this book so tremendously satisfying for fans. Up until now, the books have been top-notch formula fiction. But with this concluding chapter, author Rick Riordan raises the whole series into that timeless realm of children's fantasy fiction that's likely to last well beyond its current popularity.

From the Book:
Inside, a row of yellow turbines the size of grain silos churned and hummed. Pressure gauges and computer terminals lined the opposite wall. A telkhine was hunched over a console, but he was so involved with his work, he didn't notice us. He was about five feet tall, with slick black seal fur and stubby little feet. He had the head of a Doberman, but his clawed hands were almost human. He growled and muttered as he tapped on his keyboard. Maybe he was messaging his friends on uglyface.com.

I stepped forward, and he tensed, probably smelling something was wrong. He leaped sideways toward a big red alarm button, but I blocked his path. He hissed and lunged at me, but one slice of Riptide, and he exploded into dust.

"One down," Beckendorf said. "About five thousand to go." He tossed me a jar of thick green liquid -- Greek fire, one of the most dangerous magical substances in the world. Then he threw me another essential tool of demigod heroes -- duct tape.