I went outside to get a better look, and now it was much easier. Whizzy was using the chimney too. In, out, round and round, shimmering coils of light pink. Was Whizzy pink forever now? It was a stunning colour.

Was Whizzy playing? Wild laughter bubbled up in my chest – but my next step nearly ended in disaster: Mr Clemm’s bald cat was suddenly under my feet at the garden gate. I’d almost stepped on her.

‘How on earth have you got down here?’ I whispered, crouching to stroke her. She stared up at me with her strange, bare eyes as if she was trying to understand something – and then I had a horrible thought: if Whizzy was here, and the cat was here …

And right at that moment, a big car rolled around the corner at the other end of Usher’s Place and I knew. It had to be him. My tummy crunched in on itself.

I shot back inside the house and phoned Sam from my room, but before he picked up, I went to the window. Outside our house, right next to the front gate, stood Mr Nathaniel Clemm. And he was having a really good look. I shrank back into the curtain. My chest felt like a tight knot of squashed-down panic.

Mr Clemm looked frustrated. Whizzy was visible again, and running rings around him: hiding, then appearing, then hiding again, still playing the same game. Mr Clemm glared at thin air, because as soon as he found Whizzy, it vanished. There were even circular flashes behind me, like pieces of moonlight come to life, but it was hardly worth turning my head before they were gone.

Now I totally got it all. Whizzy is attracted to me because I set it free. Mr Clemm was here to marmalise me for tampering with his stuff.

‘Yep?’ said Sam. ‘I’m nearly at the river bridge.’

‘He’s come back for me! Mr Clemm’s here again!’

My mind scrambled over a hundred frantic thoughts. There would be accusations of trespassing, maybe even damage. Criminal damage? I felt sick.

‘No way! Right. Think. You need to hide.’

‘What? But everyone knows I’m home!’

‘That won’t matter if they can’t find you.’ Sam sounded out of breath. ‘The Cloaked Strider will give up and go home. Think of a place.’

I dived into the big walk-in junk cupboard in the spare room and got behind a box of old Lego, but it was no good. I started to smell hot metal, but couldn’t work out where it was coming from. The lightbulb in the ceiling flashed on, fizzed noisily, then went off. While I was around, so was Whizzy.

I texted Sam – Can’t last in this hiding place – and dived back to my room.