‘There’s one thing I still don’t understand,’ she said. ‘Why is she trapped here? There should be a river or a stream nearby. Can’t she follow that until she gets to the sea?’

‘Oh, I know the answer to that one,’ said the ghost-girl. ‘It’s because this isn’t really a proper lake. It’s something else. Every winter the field floods and every summer it dries up again. No water actually flows in or out of it. There’s a name for it I think …’

Comprehension dawned on Cat. She remembered learning about lakes like this in school. ‘A turlough?’ she said.

The ghost-girl nodded. ‘Yes, that’s it.’

‘What happens to you in the summer?’ Cat asked.

‘We disappear too,’ the ghost-boy replied, his voice now so faint Cat almost thought she had imagined it. ‘The lake gets smaller and smaller and then things just sort of go dark for a while. Sometimes I wonder if one day we won’t come back at all.’

Cat felt the beginnings of a plan form in her mind.

‘Ok,’ she said, slowly, working out the details as she went along. ‘The Merrow wants to go home, but she’s trapped. I want my friend back. Maybe … maybe we could do a trade? Her freedom for my friend’s life.’

The ghost-girl looked sceptical. ‘Can you really do that?’

Cat didn’t know, but up until this evening she hadn’t known she could summon a Clurichaun or fight off the Dullahan. It seemed that tonight at least anything was possible, and she knew she had to try. She nodded.

‘This is a bad idea,’ said the girl. ‘I don’t think the Merrow is one for playing fair. If you ask me, you’re better off getting far away from here. She’s occupied for now, but who knows how long it will be before she gets bored again. You should get away while you still can.’

Cat didn’t move. She wasn’t going anywhere without Shane. He was a pain in the neck, and he made it clear on an almost daily basis that he didn’t want to be her friend any more, but he had come back for her when the Dullahan had her in his grasp and she would do the same for him now.

‘Please,’ she said. ‘Can you at least ask her?’

The ghost-girl looked pained, and her form was paler now. ‘I don’t know.’

‘But why?’ Cat pleaded. ‘What have you got to lose?’

The girl seemed to be struggling now, as though she were fighting against something. ‘The Merrow’s magic is calling us back. I … I have to go. I’m sorry.’

‘I can save you too!’ Cat yelled, ‘I can save all of you. I promise.’ But before either of them could utter another word, the ghost-girl disappeared. Cat stared open-mouthed as one-by-one the ghost-children were pulled back below the dark water and she was left alone.

The breeze picked up and she began to shiver. She was soaking wet and freezing and without the ghost-children’s silver soul-lights, the night seemed very dark. For the first time all evening, Cat realised that she was truly alone.