Obviously, the GPS was broken, and the bear was wrong. Or lying. But she didn’t need either the GPS or the bear. She knew at least a half dozen low-tech ways to find south. All she needed to do was head in that direction, and she’d find the station. Everything was under control. She might be deep in the ice pack, but she was alive and well. She wasn’t even cold.

She should have been cold. Her breath was condensing into crystals on the rim of her hood, but she felt hot. Her armpits were damp, and her neck itched from the many layers. It didn’t make sense. The air had to be cold enough for five-minute frostbite. It was even cold enough for a fata morgana. Dead ahead was the most magnificent example of the Arctic air’s mirages that Cassie had ever seen.

Cassie squinted at the castle as the bear carried her toward it. She’d never seen such a beautiful mirage. Spires soared above her. They shimmered in the bending light. At the tips of the spires, the ice curled into the semblance of banners, frozen midwave. She waited for it to shrink to its normal proportions: an ordinary ridge or an outcrop of ice that had been stretched by a trick of the light.

But it did not shrink or stretch. It shone like a jewel in the sunlight. Cassie felt her gut tighten. It had to be an iceberg frozen in the pack ice—it was as white as a moonstone, while the sea ice encircling it was a brilliant turquoise—but she had never heard of an iceberg in such old ice, except near Ellesmere, on the opposite side of Canada. She studied the GPS, which continued to display its nonsensical reading. Even at the phenomenal speed the bear had traveled, she could not have crossed the thirteen hundred miles to the North Pole… Could she have?

No. It simply wasn’t possible. There had to be another explanation, a rational and scientific explanation. She slid the GPS back into her parka.

Looking up again, she saw a blue wall of ice around an opalescent castle. “Oh,” she said faintly. It was not a fata morgana. She tilted her head to see the banner-crowned spires that rose behind the wall.

“Welcome to my castle,” the bear said.

There couldn’t be a castle in the Arctic. The whole expanse had been covered by satellite photography. Someone would have seen a castle.

It was, she thought, beyond beautiful.

The polar bear brought her through an archway of blue ice into the castle grounds. Ornate turrets and overhanging arches glittered above her. Before her, a great door, a twenty-foot crystal lattice, tinkled like a thousand champagne flutes clinking in a toast as it swung open. The bear carried her inside.

Inside… took her breath away. She was inside a rainbow. Chandeliers of a million shards of ice danced colors over the foyer. Ice frescoes covered the walls, swirling with sapphire and emerald reflections. Frozen ruby red roses wound up columns. GPS forgotten, impossibility forgotten, Cassie lowered her face mask and pushed back her hood. Strangely, her cheeks stayed warm. Lifting her goggles, she squinted at the sparkles. She had never seen anything so magnificent. Her imagination could not have created this. She slid off the bear’s back and walked over to the wall. It was too vivid, too detailed to be a hallucination. She reached toward it and stopped an inch away.

What if it wasn‘t real?

“Are you going to free my mother now?” She asked.

The bear was behind her. “Once we have made our vows, I will see to it,” he said. “I cannot contact the trolls directly—they are beyond my region—but I will send word with the wind.”

She couldn’t tear her eyes from the rainbowed ice wall. “Vows?” She said.

“Do you, Cassandra Dasent, swear by the sun and the moon, the sea and the sky, the earth and the ice, to be my beloved wife from now until your soul leaves your body?”

Until my soul leaves my body. Until death, he meant. His beloved wife until death. Cassie swallowed hard. “Is this… Is this how we complete the bargain?”

“Yes,” he said.

He said it so matter-of-factly. Yes, this will fulfill the bargain. Yes, this will bring your mother back to life.

Cassie took a deep breath and laid her mittened hand on the ice wall. It felt solid and real. All at once, she couldn’t help but believe: Her mother was alive and about to be rescued. All she had to do was say the word. So simple, so easy. “All right. I do.”

“You must say the vows back to me now,” he said.

Somehow, that seemed worse. She couldn’t really marry him. Years from now, she was supposed to marry some researcher, some scientist who loved the Arctic as much as she did. She sometimes daydreamed about starting her own research station, where she and her future husband would lead expeditions together. Or maybe she wouldn’t marry at all. Like Gram, she’d be an old lady with a dozen suitors. Regardless, she was not supposed to marry a talking bear.

But it wasn’t a real wedding. It was only words. She didn’t have to mean them. She just had to say them, and she would accomplish what no one else—her father, her grandmother, no one—had been able to accomplish: She’d bring her mother back! “Do you…” She halted. “What’s your name?” She turned to look at him. His massive head was inches from her shoulder. Instinctively, she flinched. She couldn’t do this. He was… She didn’t know what he was: magic or monster, predator or rescuer.

“You may call me Bear,” he said.

“Bear,” she repeated. She was marrying a creature simply called Bear to save a woman she’d never known.

That was the crux of it: a woman she had never known. Cassie had never known her mother. All she had to do was say a few words, and she could change that. Her mother would live again.

Looking into his black eyes, she began. “Do you, Bear, swear by the sun and the moon…” After this was done, she would demand to go back. He didn’t want an unwilling wife. She knew Gram’s story. He’d said so himself to her mother, I would not have an unwilling wife. He wouldn’t refuse Cassie. She’d divorce him as quickly as she’d married him. “The sea and the sky…” She could divorce him, right? Her voice faltered. She felt a roaring in her ears.

“The earth and the ice,” he prompted.

“The earth and the ice,” Cassie said. It was almost done. What did it mean to marry the Polar Bear King? Her eyes flicked to the door—the crystal lattice shimmered like a thousand stars in a net—and then back to the bear.

“To be my beloved husband from now until your soul leaves your body,” he encouraged her.

“And you’ll bring back my mother?” she said.

“Yes,” he said. “Our vows are void if I fail.”

Cassie closed her eyes. She had to do it for her four-year-old self, who had believed with all her heart that her mommy was in a troll castle. “Fine. Let’s finish this. To be my beloved husband from now until your soul leaves your body?”

“I do,” he said.

She thought she heard a sound like a bell, but she didn’t hear it in her ears. She heard it inside, as if it were resonating in her rib cage. Her knees wobbled.

“Do not be afraid,” he said softly. “As long as these walls are standing, nothing here will harm you.”

Eyes closed, she tried to breathe. It felt as if there weren’t enough oxygen.

“Come,” he said.

Cassie opened her eyes to see the bear walking down the shimmering hallway. For a second, she didn’t move. She looked back over her shoulder at the outside world, and then she took a deep breath and followed the bear.

The corridor widened into a golden and glowing banquet hall. The faceted walls glittered so brightly with candlelight from the chandeliers that Cassie saw sparkles when she blinked. Translucent, the cathedral ceiling glowed like stained glass. She looked around her in wonder. Carved birds and animals decorated the walls and ceilings. Buttresses arched over statues. A banquet table stretched the length of the hall with thronelike ice chairs on either end. It looked like… She tried to think of places to compare it to, and failed. It was as if every beautiful ray of light, every beautiful shape of ice that she had ever seen, were here all at once.