Holly dumped her schoolbag on the floor. Hooked a thumb under her lapel, to point the crest at me. Said, ‘I go to Kilda’s now.’ And watched me.

St Kilda’s: the kind of school the likes of me aren’t supposed to have heard of. Never would have heard of, if it wasn’t for a dead young fella.

Girls’ secondary, private, leafy suburb. Nuns. A year back, two of the nuns went for an early stroll and found a boy lying in a grove of trees, in a back corner of the school grounds. At first they thought he was asleep, drunk maybe. The full-on nun-voice thunder: Young man! But he didn’t move.

Christopher Harper, sixteen, from the boys’ school one road and two extra-high walls away. Sometime during the night, someone had bashed his head in.

Enough manpower to build an office block, enough overtime to pay off mortgages, enough paper to dam a river. A dodgy janitor, handyman, something: eliminated. A classmate who’d had a punch-up with the victim: eliminated. Local scary non-nationals seen being locally scary: eliminated.

Then nothing. No more suspects, no reason why Christopher was on St Kilda’s grounds. Then less overtime, and fewer men, and more nothing. You can’t say it, not with a kid for a victim, but the case was done.

Holly pulled her lapel straight again. ‘You know about Chris Harper,’ she said. ‘Right?’

‘Right,’ I said. ‘Were you at St Kilda’s back then?’

‘Yeah. I’ve been there since first year.’

And left it at that, making me work for every step. One wrong question and she’d be gone, I’d be thrown away: got too old, another useless adult who didn’t understand. I picked carefully.

‘Are you a boarder?’

‘The last two years, yeah.’

‘Were you there the night it happened?’

‘The night Chris got killed.’

Blue flash of annoyance. No patience for pussyfooting, or anyway not from other people.

‘The night Chris got killed,’ I said. ‘Were you there?’

‘I wasn’t there there. Obviously. But I was in school, yeah.’

‘Did you see something? Hear something?’

Annoyance again, sparking hotter this time. ‘They already asked me that. The Murder detectives. They asked all of us, like, a thousand times.’

I said, ‘But you could have remembered something since. Or changed your mind about keeping something quiet.’

‘I’m not stupid. I know how this stuff works. Remember?’ She was on her toes, ready to head for the door.

Change of tack. ‘Did you know Chris?’

Holly quieted. ‘Just from around. Our schools do stuff together; you get to know people. We weren’t close, or anything, but our gangs had hung out together a bunch of times.’

‘What was he like?’

Shrug. ‘A guy.’

‘Did you like him?’

Shrug again. ‘He was there.’

I know Holly’s da, a bit. Frank Mackey, Undercover. You go at him straight, he’ll dodge and come in sideways; you go at him sideways, he’ll charge head down. I said, ‘You came here because there’s something you want me to know. I’m not going to play guessing games I can’t win. If you’re not sure you want to tell me, then go away and have a think till you are. If you’re sure now, then spit it out.’

Holly approved of that. Almost smiled again; nodded instead.

‘There’s this board,’ she said. ‘In school. A noticeboard. It’s on the top floor, across from the art room. It’s called the Secret Place. If you’ve got a secret, like if you hate your parents or you like a guy or whatever, you can put it on a card and stick it up there.’

No point asking why anyone would want to. Teenage girls: you’ll never understand.

‘Yesterday evening, me and my friends were up in the art room – we’re working on this project. I forgot my phone up there when we left, but I didn’t notice till lights-out, so I couldn’t get it then. I went up for it first thing this morning, before breakfast.’

Coming out way too pat; not a pause or a blink, not a stumble. Another girl, I’d’ve called bullshit. But Holly had practice, and she had her da; for all I knew, he took a statement every time she was late home.

‘I had a look at the board,’ Holly said. Bent to her schoolbag, flipped it open. ‘Just on my way past.’

And there it was: the hand hesitating above the green folder. The extra second when she kept her face turned down to the bag, away from me, ponytail tumbling to hide her. Not ice-cream-cool and smooth right through, after all.

Then she straightened and met my eyes again, blank-faced. Her hand came up, held out the green folder. Let go as soon as I touched it, so quick I almost let it fall.

‘This was on the board.’

The folder said ‘Holly Mackey, 4L, Social Awareness Studies’, scribbled over. Inside: clear plastic envelope. Inside that: a thumbtack, fallen down into one corner, and a piece of card.

I recognised the face faster than I’d recognised Holly’s. He had spent weeks on every front page and every TV screen, on every department bulletin.

This was a different shot. Caught turning over his shoulder against a blur of spring-green leaves, mouth opening in a laugh. Good-looking. Glossy brown hair, brushed forward boyband-style to thick dark eyebrows that sloped down at the outsides, gave him a puppydog look. Clear skin, rosy cheeks; a few freckles along the cheekbones, not a lot. A jaw that would’ve turned out strong, if there’d been time. Wide grin that crinkled his eyes and nose. A little bit cocky, a little bit sweet. Young, everything that rises green in your mind when you hear the word young. Summer romance, baby brother’s hero, cannon-fodder.

Glued below his face, across his blue T-shirt: words cut out of a book, spaced wide like a ransom note. Neat edges, snipped close.

I know who killed him

Holly watching me, silent.