‘A what?’ asked Cat, confused by the term.

‘Surely I’ve told you about stocks?’

Cat shook her head.

‘My fault,’ said Granny with a sigh. ‘I’m getting forgetful in my ould age. I really should have warned you of such things before now. A stock is a kind of changeling, but where most changelings are either fairy babies or elders made to look like the human child they’re replacing, a stock is a creature made from wood or stone. It looks exactly like the real child, but it has no heart, no soul. It’s not really alive at all.’

Cat shuddered. She didn’t know which kind of changeling sounded worse. ‘And that’s what happened to Nancy?’

Granny nodded. ‘I’m almost sure of it. It was the way that thing looked at me. I could tell there was nothing going on inside its mind at all. It stared at me for a what felt like an age before it finally turned away. It never spoke a word to me, nor anyone else from what I can gather.

‘Afterwards, the thing that looked like Nancy started coming to school less and less until one day, I heard she had died. Not one bite of food nor sup of water had passed that creature’s lips since the day the real Nancy disappeared and over time it wasted away to almost nothing. Her poor parents were heartbroken of course, but as far as I know they never learned the truth that Nancy had followed the fairy music that Halloween night and had been taken away for good.

‘The next year I lived in fear that they would come back to take a few more of us away, but they never did. They were the Trooping Fairies, you see. They travel the length and breadth of the country holding their annual Revels. I never thought I would live to see the day when they would return to Clonbridge.’

It was fully dark when Granny finished her tale and Cat shivered.

‘Caitriona,’ Granny said, losing the faraway look in her eyes and grasping Cat by the shoulder with surprising intensity. ‘I need you to remember something important. The fairy Revels last from dusk on Halloween night until dawn the next morning. Once the sun peeks over the horizon, their power wanes and they slip away to the land of the Sídhe for another year. You need to promise me that for the next few nights you’ll be extra careful. If you hear the fairy music, block your ears. If there’s a scratching at your window, don’t look out, and once the sun has dipped below the horizon, under no circumstances should you set foot outside. Do you understand me?’

‘But Granny, I promised my friends we would go trick-or-treating tomorrow. Surely with that many people about they wouldn’t–’

‘You will not leave this house!’ Granny snapped. ‘Promise me.’

Cat hesitated, she hated lying to Granny, but if it made her feel better …

‘I promise,’ she said.