She snorted. "But the sea cows all died lifetimes ago. The Lost hunted them even harder than they hunted us. That’s what the Cycle says—"

"The Cycle isn’t always right."

"Have you ever seen a sea cow?"

"No," he said. "But I’ve never seen the back of my own head either. Doesn’t mean to say it doesn’t exist." He thrust his trunk back into the sea and continued his plaintive call.

Reluctantly she ducked her ear back under the water.

The sea had its own huge, hollow noises, like an immense, empty cavern. She heard the voices of seals: birdlike chirrups, long swooping whistles, and short popping cries that the seals bounced off the ice sheets above them, using the echoes to seek out their airholes. Then, deeper and more remote, were the groans of whales, and still deeper, calls that might come from half the world away…

And — briefly — they heard a series of low whistles, interspersed with high-pitched squeaks and squeals.

But the sound died away.

They lifted their heads out of the water. They looked at each other.

"It was probably only an echo," she said. "Some undersea cliff."

"I know. There’s nothing there. But wouldn’t it have been wonderful if—"

"Come on. Let’s go and get warm."

They turned and splashed their way out of the water. Silverhair shook her head to rid it of the frost that was forming. To get their blood flowing through their chilled skin once more, they played: they chased each other across the shingle, mock-wrestled with their trunks, and gamboled like calves.

Silverhair looked back once, at the place where they had called to the sea cows.

Far out in the Channel she thought she could see something surface: huge, black, sleek. Then it was gone.

It was probably just a trick of the light.

When they were warm they continued along the beach, in search of the peculiar creatures Silverhair had spotted.

Hundreds of guillemots were arriving on the cliffs above them. This first sign of the summer’s burst of fecundity seemed incongruous on such a bitterly cold morning; in fact, the nesting ledges were still covered in snow and ice. But the seabirds had to start early if they were to complete their breeding cycle before, all too soon, the snow of winter returned. And so the birds clung to the cliffs and fought over the prime nesting sites. So intense were these battles, Silverhair saw, that two birds, locked together beak to bloody beak, fell from the high cliffs and dashed themselves against the sea ice below.

Fast as a spray of blown snow, an Arctic fox darted forward and grabbed both birds, killing them immediately. The fox buried his catch in the ice, and returned to the foot of the nesting cliff in search of more pickings.

From a snowbank high on the cliff a female polar bear, her fur yellow-white, pushed her way out of her den. She yawned and stretched, and Silverhair wondered if it was the bear she had seen before.

The bear clambered back up to her den and sat by the entrance. After a time a cub appeared — small, dumpy, and dazzling-white — and it greeted the world with terrified squeaks. A second cub emerged, then a third. The mother walked confidently down the steep cliff toward the sea while the cubs looked on with trepidation. At last two of the cubs followed her, gingerly, sliding backwards, their claws clutching the snow. The other stayed in the den entrance and cried so loudly its mother returned with the others, and she suckled all three in the sun. Then the bear walked steadily down to the sea ice — in search of her first meal since the autumn — and her cubs clumsily followed.

The mammoths walked around a rocky spur, and they came to the Nest of Straight Lines.

Lop-ear slowed, his eyes wide, his trunk held up in the air, his good ear cocked, alert for danger.

Silverhair was trembling, for this was an unnatural place. Still, she said, "We have to go on. The strange ice floe, whatever it was, must have come to rest farther on than this. Come on."

And without allowing herself to hesitate, she set off along the beach. After a few heartbeats she heard Lop-ear’s heavy steps crackling on the shingle as he followed.

In this mysterious place, set back from the beach, a series of blocky shapes huddled against the cliff. They were dark and angular, each of them much larger even than a mammoth. The great blocks were hollowed out. Holes gaped in their sides and tops, allowing in the low sunlight; but there was no movement within.

Lop-ear said, "Those things look like skulls to me."

Looking again, she saw that he was right: skulls, but with eye sockets and gaping mouths made out of straight lines, and big enough for a mammoth to climb inside.

"They must be the skulls of giants, then," she said.

The most horrific aspect of the place was that the whole of it was constructed of hard, straight lines. It was the lines that had earned the place its mammoth name, for aside from the horizon line and the trunks of trees, there are few long, straight lines in nature.

In the center of the Nest there was a great stalk: like the trunk of a tree, but not solid, made of sticks and spars through which Silverhair could see the pale dawn sky. And at the top of the stalk there were a series of big round shells, like the petals of a flower — but much bigger, so big they looked as if a mammoth could clamber inside.

The mammoths peered up at the assemblage of brooding forms, dwarfed.

"Perhaps those things up there are the ears of the giants who lived here," said Lop-ear, awed.

"But what happened to the giants?"

"You know what Eggtusk says."

"What?"

"That this place has nothing to do with giants," he said.

"Then what?"

"Lost," said Lop-ear. "The Lost made this."

And as he spoke the name of the mammoths’ most dread enemy of the past, it was Silverhair’s turn to shiver.

By unspoken agreement they hurried on.

A flat sheet lying on the shingle briefly caught Silverhair’s eye. It looked at first like a broken sheet of ice — but as she came closer, she saw that it was made of wood — though she knew of no tree that produced such huge, straight-edged branches.

There were markings on the sheet.

She slowed, studying the markings. The patterns reminded her oddly of the scrapings Lop-ear had made in the frost. There was a splash of yellow, almost like a flower — or like a star, cupped in a crescent Moon. And beneath it, a collection of lines and curves that had no meaning for her:

She wanted to ask Lop-ear about it; perhaps he would understand. But he had already hurried ahead, and she didn’t want to linger alone in this unnatural place; she ran to catch him up.

With the Nest of Straight Lines behind them, they approached the half-frozen sea.

"What I saw must have been about here," said Silverhair, trying to think.

Lop-ear looked around and raised his trunk. "I can’t smell anything."

The two mammoths walked a little way onto the ice, which squeaked and crackled under them. The ice that clung closest to the shore, where the sea was frozen all the way to the bottom, was called landfast ice. It formed in protected bays, or drifted in from the sea. Its width varied depending on how deep the water was. Later in the summer the landfast ice would break free and melt, or drift away with the pack ice.

The pack ice was the frozen surface of the deeper ocean. It was a blue-white sheet crumpled into pressure ridges, like lines of sand dunes sculpted in white. Farther away from the land Silver-hair could see black lines carved in the ice: leads, cracks exposing open water between the loose mass of floes. As the spring wore on, the leads would extend in toward the coast, splitting off the ice floes. The floes would break up, or be washed out to open sea by the powerful current that ran between the Mainland and the Island.