I bent down, picked up a rock the size of a tennis ball and hefted it, assessing its weight. Igor laughed. But I wasn’t going down without a fight and he didn’t realise he was dealing with the captain of the school cricket team. Let’s see how funny he found it when he was wearing a chunk of granite in his teeth. I bowled it overarm, aiming at his head. But throwing a rock is not the same as throwing a cricket ball. It fell short. I was out of practice.

Out of practice and out of luck. I scrabbled among the stones at my feet, searching desperately for another likely missile. Too small would do no damage, too big would be impossible to lift. My hand closed on one, sharp and pointed, barely more than a chip. I stood up and aimed it like a skimming stone, straight at Igor’s head. It spun through the air and struck him on the cheekbone. He bellowed, stopping to clutch at his face. When he took his hand away I could see a trickle of blood. He snarled and broke into a stumbling run towards me. Frantically I hunted for another stone, my breath coming in short, panicky gasps.

As I struggled to dislodge a rock lodged between two roots, a long mournful howl echoed across the moor. For a moment I froze, then looked up. Igor and Vlad hesitated, glanced uncertainly at one another. Then there was silence, the only sound was the faint mewing cries of the buzzards, circling in the sky above. They shrugged and started towards me again, Vlad grinning as his hand closed more tightly around his knife. I clawed at the rock by my feet, scrabbling with my fingers, tearing my nails as I fought to prise it loose from the earth.

But something had heard those blasts Igor had made on the silent whistle. Something was answering the call. Another baleful moan sounded, only this time it was closer. A thing unseen was crashing through a stand of nearby bracken, making the ferns rustle and wave wildly, a thing that growled and snarled and sent the sheep scattering in all directions. The bracken parted and a great black shape came thundering out.

It stopped in front of them, blocking their way: a mass of quivering muscle, fur bristling around mighty shoulders and ridging along its spine, its torn ears flattened against a broad skull, lips drawn back from fearsome fangs. It growled, rumbling rage deep in its throat, fury blazing hot in its eyes.

‘Duke!’ I whispered in awe.