They chased the intruder out on to the plains. Snowball made the steep climb up the ridge from the basin, lurching through mounds of banking snow. He stumbled to the top, wearied and whinnying. But the snow grew thinner on the spine of the hill and as the intruder’s horse made pace across the flat lands beyond, Snowball came up to speed. A sudden jolt, a jump and they left the fires of Yellowstone behind them and took up the hunt.

Cooper leaned into the horn of the saddle, whip-cracking the reins. Strands of golden hair lashed Peter’s face. The snow too, which came twisting out of the sky to strike his skin. Ahead of them, the black horse was a shadow moving at speed out across the plains. Every now and then it took a sudden turn, veering left and right, navigating tufts of frozen grass and hillock. But nothing broke its pace. It leaped across a cleft in the ground, clearing a grove of pines and ran on. An owl took off from its vantage point inside the woods. Snowball galloped beneath the boughs and Peter glanced back, watching the bird’s white wings take flight. A ghost with a moon for a face, travelling out across the frozen wastes.

The plains howled, driving shards of whisking snow from the earth. The sun vanished beneath the blizzard and the stranger’s horse increased its gallop. A black bullet, streaming through the dizzying vortex. Cooper flicked the reins, geeing Snowball on, and tightened the distance between them.

The stranger’s horse maintained its lead. But it hadn’t gone much further when a grey mass broke from inside the slaughtering snow. The horse recognized the huddled mound of ashen flesh and bone for what it was and reared up, quickly changing its course again. It struck down with clashing hooves, galloping deeper across the plains. Cooper tugged on the reins and Snowball made the adjustment, arching round to keep clear of the herd, then carried on his pursuit.

“They followin’?” Cooper hollered.

“No!” Peter cried, craning around. Then, “Yeah. They’re coming.”

A wall of featureless sludge surged across the pristine snow and the Restless Ones took up the chase.

Snowball pushed on, increasing his pace. But the plains were as endless as the sky and Snowball was beginning to tire. Peter held on a little tighter to Cooper’s waist and leaned out. There was no sight of a forest or river ahead of them. Nothing to break the race. Nothing to break the stranger’s increasing lead. But just when Peter was about to call out for Cooper to give up the hunt, something changed.