This story is also included in "The Demigod Files," so non-UK fans will also be able to get their hands on the it.

Christmas in the underworld was not my idea. If I had known what was coming, I would have called in sick. I could have avoided an army of demons, a fight with a titan, and a trick that almost got me and my friends killed. But no, I had to take my stupid English exam.

So there I was, the last day of winter break sitting in the auditorium with all the other freshmen, when Mrs. O'Leary burst onto the stage, barking like crazy. Mrs. O'Leary is my pet hellhound. She is a shaggy black monster, about the size of a hummer. She's got razor fangs, steel sharp claws, and glowing red eyes. She is really sweet, but she usually stays at Camp Half-Blood.

I was a little surprised to see her on the stage, trampling over Christmas trees, Santa's elves, and the rest of the winter wonderland set. Everyone looked up. I was sure the other kids were going to panic and run for the exits, but they just started laughing.

A couple of the girls said, "Aw...cute."

Our English teacher, Dr. Boring, (I'm not kidding, that's his real name) adjusted his glasses and frowned.

"Alright," he said, "whose poodle?"

I sighed with relief. Thanked gods for the mist, a magical veil that keeps humans from seeing things the way they really are. I'd seen it bend reality plenty of times before, but Mrs. O'Leary as a poodle? That was impressive.

"Uh... my poodle, sir." I spoke up. "Sorry, she must have followed me."

Somebody behind me started whistling "Mary had a little lamb". More kids cracked up.

"Enough!" Dr. Boring snapped. "Percy Jackson, this is a final exam, I cannot have poodles..."

Woof!

Mrs. O'Leary's bark shook the auditorium. She wagged her tail knocking over a few more elves. Then she crouched on her front paws and stared at me, like she wanted me to follow.

"I'll get her out of here, Dr. Boring." I promised, "I'm finished anyway."

I closed my test booklet and ran toward the stage. Mrs. O'Leary bounded for the exit and I followed. The other kids were still laughing and calling out behind me, "See you, poodle boy!"

Mrs. O'Leary went straight into Carl Shirts Park. By the time I caught up to her, she leaped an iron fence and disappeared into the bushes. On the other side was a clearing. Mrs. O'Leary was sniffing around, wagging her tail like crazy. I wasn't sure why, but the back of my neck started to tingle. I took out my ball point pen, and uncapped it. Immediately it grew into my bronze sword, Riptide.

Then, the bushes rustled and a figure in a hooded parka stepped into the clearing, an arrow notched in her bow. The girl aimed at me and froze.

"Percy?" She pushed back her silvery hood. Her black hair was a little longer than I remembered, but I knew those bright blue eyes, and the silver tiara that marked her as the first lieutenant of Artemis.

"Thalia?" I said, "What are you doing here?"

Before she could answer, a cloud passed over the sun. I readied my sword. Thalia drew her bow. Instinctively we stood back-to-back. A patch of darkness passed over the clearing, and a boy tumbled out of it, like he'd been tossed.

"Ow!" he muttered.

He brushed off his aviator's jacket. He was about twelve years old, with dark hair, jeans, and a black t-shirt, and a silver skull ring on his hand. A sword hung at his side.

"Nico?" I said.

Thalia's eyes widened, "Bianca's little brother?"

"Why did you bring me here?" he grumbled," One minute I'm in a graveyard, the next... is this New York? What in Hades name am I doing in New York?"

"We didn't bring you here," I promised. "We..." And then a shiver went down my back. "The children of the Big Three." I said, "Zeus, Poseidon, Hades."

Thalia took a sharp breath. "The prophecy. You don't think..." She never finished the thought.

The ground rumbled. Nico drew his sword, a black blade of Stygian iron. Mrs. O'Leary barked and leaped backwards in alarm. Too late. I realized she was trying to warn me.

The ground opened underneath Thalia, Nico, and me, and we fell into darkness...