‘Alison will take an antihistamine and will be fully recovered within an hour or two. The rest of you will go to your common rooms and will write me a three-hundred-word essay on allergy triggers, to be done by tomorrow morning. I am disappointed in all of you. You are old enough and intelligent enough to deal with this kind of situation with good sense rather than silliness and hysteria.’

McKenna took one hand off Alison’s shoulder – Alison slumped against the wall – and pointed down the corridor. ‘You may go now. Unless any of you have anything useful to share?’

‘Miss,’ Joanne said. ‘One of us should stay with her. In case—’

‘No, thank you. Common rooms, please.’

They went pressed together in clumps, arm-linking and whispering, throwing back glances. McKenna stared them out of sight.

Said to us, ‘I assume you realise what caused this.’

‘Haven’t a notion,’ said Conway. She moved in, between McKenna and Alison, till McKenna let go. ‘Alison. Did anyone say something about Chris Harper’s ghost, before you went to the toilet?’

Alison was white and purple-shadowed. She said faintly, ‘He was in that door. Doing pull-ups off the top of the frame. His legs were waving.’

Always doing something, Selena had said. I don’t believe in ghosts. Felt the shiver rise up between my shoulder blades anyway.

‘I think maybe I screamed. Anyway he saw me. He jumped down and came running down the corridor, really fast, and he grabbed me. He was laughing right into my face. I screamed more and I kicked him, and he disappeared.’

She sounded almost peaceful. She was wrung out, like a little kid after puking its guts.

‘That will do,’ McKenna said, in a voice that could have scared grizzlies. ‘Whatever allergy trigger you touched, it caused a brief hallucination. Ghosts do not exist.’

I said, ‘Is your arm sore?’

Alison gazed at her arm. ‘Yeah,’ she said. ‘It’s really sore.’

‘Unsurprisingly,’ McKenna said coldly. ‘And will continue to be until it is treated. On which note, Detectives, please excuse us.’

‘He smelled like Vicks,’ Alison told me, over her shoulder as McKenna marched her off. ‘I don’t know if he used to smell like Vicks before.’

Conway watched them go. Said, ‘What’s the betting the Ugg kids spread the word we were in their common room?’

‘No takers. And it had plenty of time to get round.’

‘To Joanne. Who had to guess what we were after.’

I nodded after Alison. Footsteps rattling around the stairwell, echoing; her and McKenna were taking the stairs at a snappy old pace. ‘That wasn’t put on.’