Alison shifted it away from me. ‘It’s OK. Thanks.’

‘Let’s see,’ Conway said.

Alison shot a glance at McKenna: she’d been told not to show it. McKenna nodded, reluctantly.

Alison pulled up her sleeve. The blisters were gone, but the skin where they’d been still had a bumpy look to it. The handprint had faded to pink. Alison had her head turned away.

‘Nasty,’ I said sympathetically. ‘My sister used to get allergies. Up her face and all, once. Turned out it was the washing powder our mammy was using. Did you figure out what did that, no?’

‘The cleaners must have switched to a new brand of hand soap.’ Another glance at McKenna. Another line learned off by heart.

‘Yeah,’ I said. ‘Must’ve done.’ Shared a look with Conway, let Alison catch it.

Alison tugged down her sleeve and started scooping up her books. Glanced once round the room, big-eyed, like we’d turned it into somewhere strange and untrustworthy, before she scuttled out.

McKenna said, ‘If you should wish to speak to me, Detectives – or to any more of the fourth-years – you will find us in the common room.’

Meaning the nun had ratted us out. McKenna was taking over the fourth-years, damage control or no, and we were getting no more interviews without an appropriate adult.

‘Miss McKenna,’ I said. Held out a hand to keep her back, while Alison straggled down the corridor towards the common room. Even on her own, the kid walked like she was trailing after someone. ‘We’ll need to speak to some of the girls without a teacher present. There are elements of this case that they wouldn’t be comfortable discussing in front of school staff. It’s only background to the investigation, but we need them to speak freely.’

McKenna was opening her mouth on Absolutely not. I said, ‘If unsupervised interviews are a problem, obviously, we can have the girls’ parents come in.’

And start last year’s flap again, parents outraged, panicking, threatening to pull their daughters out of Kilda’s. McKenna swallowed the No. I added, for good measure, ‘It would mean we’d have to wait till the parents can get here, but it might be a good compromise solution. The girls would probably be more comfortable discussing breaches of school rules in front of their parents than in front of a teacher.’

McKenna shot me a look that said You don’t fool me, you little bastard. Said, salvaging, ‘Very well. I will allow unsupervised interviews, within reason. If any girl becomes distressed, however, or if you receive any information that affects the school in any way, I expect to be informed immediately.’

‘Of course,’ I said. ‘Thanks very much.’ As she turned away, I heard the surge of voices from the common room, hammering around Alison.

‘That arm’s gone down some more,’ Conway said. She tapped Joanne’s bedside locker. ‘Fake tan in there.’