Later, when I turn the corner into St Matthias Road, I can see right away that Dad’s van isn’t there, thank goodness. I haven’t had chance to tell Sergei to keep his mouth shut about what happened with Linford today. I just hope he’s not stupid enough to blurt it out before I speak to him.

I keep everything crossed that Sergei and his mum are out, too. I really need some time to think things through.

I feel like I’m in a bubble, separate from everyone around me. All alone, even when there are people around.

As I turn the key in the flat door and push it open, my ears fill with the strains of music floating down the hallway. It sounds like the same kind of dull music that Mr Fox plays while we file into our Monday morning assemblies.

I kick off my shoes, dump my rucksack by the door and creep down the hall, looking into the rooms. It looks like Dad and Angie are out, but Sergei is holed up in my bedroom.

When I get closer, the notes are so loud and clear I spy through a crack in the door to make sure Sergei hasn’t moved an actual piano into my bedroom. It wouldn’t surprise me; he’s filled it with all sorts of weird stuff already.

But he isn’t playing the piano; he’s sitting on the bed, staring into space like a zombie. His face is blank, eyes glazed over and his lips pressed together in a spongy line, like someone just blurred his features with a soft cloth.

I stand still for a moment and listen. The piano notes dance high and bright, then ping low and fast like vibrating raindrops. My heart seems to swell and then squeeze in tight on itself. I can’t make my mind up whether I feel like laughing or crying.

I feel the music slowly building like a storm until finally it erupts into a twisting melody that swirls around the booming bass notes as if there is an entire orchestra stuffed into my tiny bedroom.

I close my eyes and let the music flow through me. Before I know it, my mind is drifting to a time last summer when Dad came home early unexpectedly for the weekend. We got up early Saturday morning, jumped in the van and drove for nearly three hours so we could have fish and chips for our lunch, sat on a wall in Whitby harbour.

There’s a flurry of melancholy notes and another memory floats by. The day Mrs Brewster’s Labrador, Frank, got knocked over in the street by a motorbike. While someone went to fetch Mrs Brewster, I sat down beside Frank in the road and cushioned his soft, velvety head in my lap until his rasping, furry chest finally lay still.

I blink hard a few times.

I don’t know why I’m suddenly thinking about this stuff; it’s crazy. Sergei’s music is seeping into my head like a wisp of black magic, turning my sensible thoughts to mush.

The bedroom door whips open.

‘Calum, why are you standing out here? Come in and listen.’

‘I don’t need an invite to come into my own bedroom, thanks,’ I shout over the music.

I push by him and flop down on to my bed. I pick up one of my DVDs and pretend to read the blurb on the back, but the words don’t make much sense.

‘You were listening to the music just now.’ He raises his voice above the notes.

‘Waiting until it finished, more like.’ I kick off my shoes without sitting up. One of them hits the small portable speaker his phone sits on and the track jumps.

‘How is your jaw?’

‘It’s fine.’ I’m trying to ignore the aching. ‘So don’t go blabbing to Dad about what happened this afternoon.’

‘Should I turn it off, the music?’

‘Please yourself.’

He reaches over and turns the volume down.

‘Do you like Chopin?’ He pronounces it Show-pan.

‘What?’

‘Frédéric Chopin,’ he says again. ‘The composer. He was born in Warsaw. This piece is called Nocturne Number 19 in E minor.’

I sigh, and study the cover of the DVD.

‘This piece of music, it is one of his twenty-one Nocturne compositions.’

‘Fascinating.’ I scowl at him. ‘You seem to know an awful lot about nothing.’

My insults seem to slide off him like oil.

‘Chopin very quickly gets inside here, Calum.’ He taps his heart space. ‘I can see in your face that he got you, too.’

I’ve lost one of my best friends today because of him and his mum turning up where they’re not wanted, and now he’s sitting there grinning at me like an imbecile.

‘Why don’t you just sod off back to where you came from?’

I feel a twist inside when I realize I sound just like Linford. I half slide, half fall off my bed and kick the speaker over in the process. The music jumps, then stops completely.

‘Hey, what the hell is wrong with you?’ He takes a step towards me. ‘You should learn some manners.’

‘Oh yeah?’ I glance at his clenched hands. ‘And who’s going to teach me some? You?’

I square up to him but the mild-mannered Sergei I see at school isn’t here. Instead I feel an undercurrent of something else coming off him and the back of my neck prickles.

‘Maybe I will,’ he says quietly. His eyes glitter, dark and dangerous. ‘Maybe I will wait for the right moment.’

Perhaps he’s just sick of tiptoeing around me, like I got fed up with Linford. I push past him.

‘Yeah, right. When you’re big enough,’ I say when I’m at a safe distance.

I slam the door and stand for a moment in the hallway, breathing heavily.

I feel ousted from my own bedroom. How did it get to this?

Sergei seems quiet and non-confrontational at school, but here in the flat I sense a different vibe. Who knows what he is really like? What if he’s leading me to believe he is harmless when really he is someone else altogether?

Sergei stays in my room all evening with the door shut.

I sit watching TV on my own in the sitting room, but I can’t relax the same, knowing he’s in there. I feel annoyed that he’s taken over my space.

At the same time there’s a thickness in my throat I can’t swallow down. I get to thinking about Amelia and her family, coming to live in a new place but made to feel like impostors. I shouldn’t have said some of the things I did to Sergei. I can’t really concentrate on the TV so I turn it off.

Dad and Angie still aren’t back. I’m just about to flick off the lamps and go to bed when I hear shouting and whistling out on the road.

I stand still and listen and a little shiver runs down both my arms. I can’t shake the uneasy feeling that now Linford will be out to get me. Dad’s not here and if there’s anyone out there wanting to cause trouble, they could put a brick through the window or even try and bash the door in.

I debate for a few moments whether to go over to the window. It could just be rowdies coming home from the pub, but it’s still a bit early – they don’t usually turn out until about eleven thirty.

Someone shouts and then there’s a piercing whistle. Whoever it is seems to have stopped right outside the flat.

I walk slowly to the loosely pulled-together curtains and peer out, down on to the road. A group of about eight lads in baseball caps and hoodies are standing right outside our flat, gathered by the front gate. In the dusk, I can’t make out individual faces under all the hoods and hats, but they look just like the troublemakers from the top end of the estate, the ones who were in the car that stopped outside the chippy. I’ve seen them roaming around like a pack of dogs before.

They look up at our window and I realize too late that with the lamps on behind me, I’m lit up like a fairy on a Christmas tree. Suddenly the group roars and points up, whistling and making unpleasant hand gestures. I’m trying to work out why they’re suddenly doing that to me when I feel something touch my shoulder. I jump back to find Sergei at the side of me, staring down at the road.

‘Get away from the window,’ I hiss, pulling him away from the glass.

I pull the curtains back together and peer down at the road through a tiny gap at the side. As the group shuffle off slowly, still laughing and staring up, they move briefly, one by one, into light as they walk under a street lamp.

The last youth stands there a moment and glares up. I can see his top lip curling and his eyes shining with a cold fury. For a brief moment, the street light illuminates his whole face.

I step back from the gap, my heart pumping hard. It’s Linford.