Walking forward to the passenger cars, she looked out the window and got a shock: The train was now traveling over open water. Miles and miles of gray waves, with no land anywhere. The air was cold and tasted like salt, and she put her conductor’s blazer back on, then went and got the winter coat too.

The train slowed and stopped, right there in the middle of the ocean. She looked around for a station, but there was nothing except water. Swells sloshed around the train’s wheels. Was it a mistake? Had they overshot the platform somehow? She leaned out as far as she could and looked forward, then back. Nothing.

A chilly wind ruffled her hair. She could see her breath in the air.

And what were the train tracks resting on? She looked down but she couldn’t see that, either. Pontoons? Some kind of underwater ridge? She had that same creepy feeling she had at the last stop: Something was off here.

We should go, she thought. She closed the doors—but as soon as the train started again, she heard a shout.

“Wait!” It was Tom, somewhere way down at the other end. “Wait! Stop the train!”

What now? Leaning out, she could see him standing on the flat car, waving frantically and pointing at something in the water. Kate ran back to join him.

He was crouched down, peering over the edge of the flat car into the ocean, so Kate looked too.

“I just saw it,” he said. “A second ago.”

“What?”

He shook his head. “I don’t know. It was—”

Something big and white came rushing up at them from underwater. Kate was so shocked she fell over backward. For a second she was sure it was a great white shark leaping out of the water to devour them both in one mouthful.

But that didn’t happen. It wasn’t a shark. It was a polar bear.

The poor thing looked exhausted—she was desperately paddling to keep her black nose above the water. With the last of her strength, the bear lunged upward and got her head and paws onto the edge of the car.

Kate and Tom grabbed double handfuls of her cold, thick, wet fur and pulled as hard as they could. The bear managed to get a hind foot onto the car, and Kate pulled on that, too. They heaved and heaved, and for a good minute there it felt like the poor thing would never make it, but finally the bear rolled and scraped and lumbered the rest of her body up onto the flat car, and all three of them collapsed, breathing hard.