There are voices outside my room, and seconds later three girls come in, wearing school uniform. Kirsten Olen, Katie Pelling and – of all people – Aramynta Fell.

The girls have been sent as a delegation from Mr Parker’s class to deliver a get-well card signed by all my classmates who are not on the adventure-centre trip to the Lake District.

There aren’t enough chairs in my room, so between them and Boydy they sort of share bed-space and the two chairs that are there.

Kirsten and Katie behave as if everything is fine, and has always been fine.

And actually – that’s OK by me.

But there’s something bugging me about Aramynta. I can’t put my finger on it. She’s even being nice to Boydy.

She’s behaving … suspiciously, I suppose. She definitely doesn’t want to be there, and it’s separate from the fact that she’s always been at the very least frosty to me, if not completely hostile. There’s something nagging at me, a memory trying to come to the surface, but I can’t quite get to it.

We’re talking about Mr Parker, and Boydy’s riot-causing Whitley’s Got Talent performance, and his pretending to be all mysterious and saying he can’t reveal the secret of his trick, when Katie says:

‘You were close to it. You saw it, didn’t you, Mynt?’

Mynt.

That’s when it comes back to me. Jesmond’s conversation in his bedroom, when he was arranging with Aramynta to claim the reward on Geoffrey.

I just blurt it out.

‘Thanks for coming. But before you go: Aramynta? How much reward money did you collect from old Mrs Abercrombie?’

And I know I’ve got her – not from what she says, but from the colour she goes, which is the brightest pink I have ever seen on anyone.

‘I … I … what?’

None of them has any idea what I’m talking about – not even Boydy. I tell them what I’ve guessed about Aramynta’s role as a ‘spotter’, delivering free newspapers and takeaway leaflets and identifying houses with pets that could easily be taken by Jesmond and Jarrow and held until a reward is offered. And if no reward is offered, it’s an easy job just to return the dogs they’ve taken.

I’m kind of making it up as I’m saying it, but I know I’m right.

Aramynta doesn’t even try to deny it. She just stares at the floor.

‘The twins are back tonight, aren’t they?’ I go on. ‘So unless you want me to go to the police – and I will, I promise – you will return the reward money to Mrs Abercrombie.’

‘You … you have no proof,’ says Aramynta. But I can tell she’s scared.

‘Oh yes we do, don’t we, Boydy?’

Boydy – who, till this point, has been watching me, astounded – snaps his mouth shut and springs to life. He reaches into his pocket and pulls out Jesmond Knight’s distinctive red-and-white-striped phone with a football crest on it.

‘Sure do,’ he says without missing a beat.

He stands up and addresses them like they’re in a court, with his lawyer’s voice. ‘Do you recognise this mobile telephone? Of course you do – it belongs to Jesmond Knight, does it not?’

‘Does it not?’ I have to bite my cheek to stop myself smiling. I can see where this is going. He’s brilliant.

Aramynta nods.

Boydy turns the phone on and starts to dial a number. ‘Oh, good,’ he says, pretending to talk to himself. ‘FaceTime seems to be working. Hello, Jarrow. How lovely to see and hear you!’

On the little screen of the phone is a stunned-looking Jarrow Knight. It looks like she’s on the school coach. There’re other people around her, but the only one I can pick out is Jesmond, who puts his face close to the phone’s camera and snarls:

‘Is that my phone, Boyd? You, my friend, are dead.’

But Boydy just grins, super-confident.

‘I don’t fink so, Jezza, me old china plate.’ He resumes his lawyer voice. ‘You see, on this very device, I found a good deal of evidence. Text records, call logs, the lot, all leading to the firm conclusion that several crimes have been committed – those of obtaining money by deception, and of holding an animal in contravention of the Domestic Animals Act of 1968. All of the evidence points to a prima facie case that the perpetrators of the said offences are Mr Jesmond Knight and his twin sister, Jarrow, of Number Forty Links Avenue, Whitley Bay.’ He stops and points a dramatic finger at Aramynta. ‘And you, Miss Aramynta Fell, are an accomplice to the crime and will be prosecuted accordingly.’

It’s a bluff – a massive bluff – but it’s enough.

Aramynta has turned white.

On the phone’s screen, Jarrow is chewing her bottom lip furiously, and blinking hard.

We’ve got them.

Boydy turns back to the phone, which he’s holding up selfie-style so that Jarrow and Jesmond can see the scene properly.

‘Prosecuted, that is, unless all the money obtained by said deception is returned to the victims within a week.’ Boydy leans close to the phone. ‘Case closed. Sort it out, will ya?’ He looks at his watch. ‘Mynt? Queenie Abercrombie can be first. You’ve got an hour until we call ’er to check it’s been done. Got it? Chop chop.’

Aramynta nods and practically runs from the room.

Boydy turns his face back to the phone, and he’s dropped the posh voice. ‘I mean it, Jarrow, Jesmond. All the money returned, or everyone gets to know – starting wiv your dad. This phone will be posted through your letter box tonight, but don’t worry – I’ve backed up all the data. Bye-bye!’ Without waiting for a response, he ends the call.

Katie and Kirsten have watched all this with mounting astonishment.

‘What a cow!’ says Kirsten.

‘Never liked her. Not really,’ adds Katie.