‘What’s that supposed to mean?’

Not-Mikey said nothing in reply. Instead, he opened his mouth wide and began to wail. Cat took a step back in surprise. That was not what she had expected.

After a few seconds, she heard her mam’s tread on the landing and she stepped into the room looking tired and bleary-eyed.

‘Cat, what are you doing up at this hour?’ she said with surprise as she picked up the inconsolable not-Mikey and hugged him close to her chest.

‘I–I heard a noise, and I thought I’d check on Mikey.’

Her mam smiled. ‘Thank you, Kitty-Cat, that was sweet of you. Why don’t you go back to bed for a while? It’s early yet and you’ll need all your energy for trick-or-treating later.’

Cat didn’t move. She didn’t like the thought of leaving her mam alone with that creature for any length of time, but her mam would start to get suspicious if she stayed. Her mam normally had to drag Cat out of bed on a Saturday morning. She couldn’t tell her what was happening – there was no way her mam would believe her – but what if she kept her mouth shut and not-Mikey did something to hurt her? Before she could make a decision, the phone began to ring.

‘Who on earth is calling us at this hour?’ asked her mam.

Cat almost smiled. It was probably Granny, calling to say she was on her way.

‘Mind him another minute will you, love?’ said her mam, thrusting the wriggling baby into Cat’s arms.

She almost recoiled at the imposter’s touch.

‘Hello, Laura Donnelly speaking,’ she heard her mam say before she closed her bedroom door.

Cat quickly set not-Mikey on the ground and glared at him with her hands on her hips.

‘That wasn’t very gentle,’ he said, brushing himself down with exaggerated movements. ‘And here was me thinking big sisters are supposed to take care of their baby brothers.’

‘You are not my brother,’ Cat hissed.

‘No,’ said not-Mikey. ‘I’m not.’

‘You’re a changeling. Granny told me all about your kind.’

‘And what if I am? What does it matter to you? From what I’ve heard, you didn’t much care for your poor little brother anyway. Maybe you’ll find me an improvement.’ The imposter’s voice changed, adopting a perfect imitation of her own, ‘‘‘Why are you always such a pain, Mikey? Why can’t you be fun and sweet like Jenny?’’’

Cat felt numb, as though she was no longer connected to her body. Those were her words; she had said them only last night when her mam had asked her to entertain Mikey for a few minutes while she washed up. To hear them now, thrown back at her from this creature that looked so like her brother in every way, each word felt like a knife.

‘Oh yes, Caitriona,’ not-Mikey continued. ‘I know what a burden he is to you. Why, you should be thanking us for taking him off your hands.’