“COME ON, HAMELA,” Hamhock whined as the sounds of the jungle slowly resumed. “Pleeeeease.” He was watching his sister climb up onto Woolly’s back.

“No, Hamhock,” she said, “you’ll be safer here.”

Echo and I had immediately agreed on a plan, and there was not a moment to waste. “Time to open our eyes,” I said, leading Woolly out of the cave.

Hamhock dashed toward us, but Stony scooped him up and held him.

Before he could whine again, Echo and I were out of the cave and thundering through the jungle on the Woolly Mammoth Express.

“Lug?” whispered Echo as we approached the looming mountain.

“Yeah?”

“Are you nervous about climbing Mount Bigbigbig?”

“No,” I said. “I’m nervous about never coming back down.”

She tittered anxiously.

“Did you feel that?” I asked.

“Cold rain?” guessed Echo, looking up at the treetops whizzing by.

It was only when Woolly began to climb the slope of the mountain and the jungle canopy gave way to bigger patches of sky that we saw the strange white flakes coming down.

“They’re beautiful!” cried Echo.

“They turn to water when you touch them!” I said.

She laughed in delight as the white flakes melted on her upturned face.

Woolly made a deep rumbling sound that sounded like SNOOOOOOOOOW.

“What?” I said.

“That must be what mammoths call this stuff!” shouted Echo over the wind.

The snow came down faster as we climbed higher. The wind gusted and wailed, lifting the strange white stuff off the ground so that the whole landscape seemed ghostly.

“How close are we?” shouted Echo.

“I’m not sure,” I said, squinting through the flurry of flakes.

Echo looked around and shivered. “Do you think it might be true what they say?”

“About the mountain?”

“About the ghosts of the banished,” she said, “wandering around, looking for the clan folk that exiled them?”

“I don’t know about ghosts,” I said, pointing across the slope. “But I’d bet my life that’s Crazy Crag’s cave over there.”

We both gazed at a little opening in a distant ridge. “Lug,” said Echo, “why is the cave’s mouth flickering like that?”

“I think it’s a trick of the eyes—from all the snowflakes dancing in front of us.”

She snuggled deeper into Woolly’s fur. “When Crazy Crag invited you up there … were you tempted to go?”

“Do I look crazy to you?”

She didn’t reply.

“He just jumped out of nowhere, cackled something about beasts and storm light, and told me to come up for a visit.”

We stared some more at the falling snow and the strange flickering cave. “So I guess you know the legend about him?” she asked.

“You mean the part about how he can turn his hands into bolts of storm light and strike down anyone who comes near him?”

“Yes,” she said, “that part.”

“That’s why we won’t be stopping by his place anytime soon,” I replied.

Then I pointed up the mountain and Woolly charged up another long stretch of steep slope. He seemed very much at home in the snow—as if he’d been made for moving through it.

As we crested the peak of Mount Bigbigbig, I looked out over the vista to the north. The most astounding sight met my eyes. An enormous herd of strange beasts was slowly making its way toward the mountain across the great white snow-covered plain below. It was like watching an entire ant colony on the move, although from their gait these appeared to be large hoofed creatures. There were several other immense herds farther back, but I couldn’t tell much about them at this distance. Then I noticed some closer but smaller packs of animals. I could make out some lumbering giant slothlike beasts, which seemed to periodically rear up on two legs. Just in front of them were shaggy creatures sporting antlers like upturned giants’ hands. I glanced over at Woolly and followed his gaze to a herd of woolly mammoths that was just starting to lumber up the north slope of the mountain.

Woolly flapped his ears, lifted his trunk, and trumpeted jubilantly.

“It’s his family!” cried Echo.

I patted Woolly’s head. “I’m happy for you,” I whispered to him.

“Lug!” said Echo. “Look in that grove.” She pointed to a dark stand of dead trees behind the mammoth herd.

I followed her finger, squinting, until I saw movement. And there they were, among the twisted tree trunks, a huge pride of saber-toothed tigers slinking their way through the shadows. “Stone it!” I muttered. “That’s a lot of cats.”

“Lug, do you have any idea what’s going on here?”

“I’m not sure,” I said. “But I think all these creatures are following the cold snow from the north.”

“But … why would anyone follow the cold?”

I touched Woolly’s thick shaggy hair. “Remember how warm it was sleeping next to him?”

She nodded.

“Now imagine if your entire body was completely covered by hair like that.”

“How charming,” she muttered. “I … guess I’d be too hot.”

“Right,” I said. “You’d be too hot, unless—”

“Unless it was getting colder and colder!”

“Exactly. And all these northern creatures have thick coats. I think they can only live where it’s cold.”

She looked out over the great snow-covered northern plain. “So … as the cold spreads from north to south … it opens up new foraging territory for them?”

“Or, if you’re a meat eater, new hunting grounds.”

“Right,” she said. “And if there aren’t any people around, the cats won’t need to compete with us for boars … or caves to shelter in—”

“Or jungle llamas,” I said, suddenly remembering. “The day before Stony and I were banished, a macrauchenia mysteriously disappeared from our village stable. Everyone blamed it on your clan, but I’d bet anything it was Smilus.”

Woolly slowly knelt on the ground—a signal for us to dismount. We did so and found ourselves ankle deep in the snow.

“Hey … Woolly?” said Echo. “Woolly!”

But he was already barreling down the hillside.

We watched him run as the saber-toothed cats crept toward his herd.

“He’s going to warn his family,” she said.

I nodded. “We’d better do the same.”