Within minutes, Miss Spinnaker pulls up in front of a little white cottage with a garden full of herbs and a wonky front gate.

They follow Polly’s teacher into the house and down the little hallway into the kitchen. It’s the first time Polly has ever been in her teacher’s house, and for some reason it makes her feel embarrassed. Like she has just caught a glimpse of Miss Spinnaker in her underwear or something.

Polly looks around the tiny kitchen. It is perfectly neat, but crowded with wonderful trinkets and floral teacups and newspapers and books piled up carefully.

At school, Miss Spinnaker seems so gracious and wise, so Polly had always imagined she might live somewhere very grand, like a palace. Not a little white cottage with a herb garden and a wonky front gate.

Miss Spinnaker gestures towards the rickety wooden table, and turns to the stove to put an old iron kettle on to boil. A sleek black cat jumps up onto the bench and Miss Spinnaker runs her hand down his body and kisses the top of his head.

Polly and Buster sit down. There is a bowl of ripe ju-ju fruits on the table and Buster stares at them longingly.

‘Help yourself,’ Miss Spinnaker says, as she jangles over to inspect Polly’s wound more closely.

Buster takes three, but Polly gives him a dark look, so he puts one back in the bowl.

Polly is impressed at how different her teacher looks out of the classroom and after her broomstick ride. Her long red hair is wild and her green eyes flash like emeralds.

Just like a real Black Witch, Polly thinks admiringly.

‘Now, let’s have a better look at this wound,’ Miss Spinnaker says, peering down at Polly’s hand. The skin around the puncture marks is red and swollen. ‘A monster’s bite can become infected very quickly if left untreated,’ she explains. ‘Just as well she didn’t bite you harder. She could have taken your whole hand off!’

‘It’s really not a serious bite,’ says Polly.

Miss Spinnaker puts a hand on Polly’s forehead. ‘All the same, you have a slight fever already.’

‘She did another spell, too,’ Buster says, his mouth full of ju-ju fruit. Purple juice trickles down his chin.

‘Polly!’ says Miss Spinnaker. She frowns and puts both hands on her hips.

‘It just came out of me,’ Polly whimpers. ‘I didn’t mean to. Mrs Halloway pointed a wand at me!’

Miss Spinnaker gasps. ‘What?’ She shakes her head and her mouth sets into a hard line. ‘A fully grown witch pointing a wand at a child? What is this world coming to?’

‘I did try to stop the spell from coming out,’ Polly says. ‘But I was scared and angry …’

‘She was protecting me again,’ Buster says, leaning his head affectionately on Polly’s shoulder and sucking purple juice off his fingers.

‘It wasn’t as big as the one in the gallery,’ Polly continues.

‘Polly. That’s two spells out of school grounds now. You know very well what three means?’

Polly hangs her head. ‘I know,’ she says. ‘Expelled from school.’

Miss Spinnaker nods. Then she softens. ‘Well, at least you appear to be less affected this time. That’s a good sign, I suppose. It hopefully means you’ll be able to control yourself soon. I would hate to see you expelled from the Academy.’

She bustles over to a wide cupboard by the sink. Inside are dozens of tiny glass jars of all different shapes, colours and sizes, filled with all manner of strange ingredients.

Miss Spinnaker hesitates for a moment, then pulls out five little bottles and carries them over to a big black cauldron sitting on her kitchen bench. She shoos the cat away and he jumps down onto the floor.

‘Actually, I have been thinking a lot about you lately.’ She turns to look at Polly again. ‘I am not absolutely sure, but I have a strong feeling you might be a Silver Witch.’

Polly scrunches up her face. ‘A Silver Witch?’

‘Cool!’ says Buster, and he reaches for another fruit.

‘Buster!’ Polly whispers. ‘You’ve already had two!’

Buster puts his hands back on his lap.

Miss Spinnaker unplugs a glass stopper from each bottle and carefully measures out ingredients into a beaker before tipping them into the cauldron. Polly recognises grout juice and bramble mix, as well as thistle weed and ground seaswell, but she can’t make out what the other things are.

‘Did your father ever give you anything special before he died?’ Miss Spinnaker asks, stirring the mixture with a long wooden spoon.

A swirl of different images flit through Polly’s mind. The star stickers. A tricycle. Dragon beads. Polly shakes her head. Nothing in particular is coming to her, but the memories rushing into her mind squeeze at her heart.

Miss Spinnaker stirs slowly, staring down into the pot. Steam has begun to rise up into the chimney. ‘No? Nothing precious, that he told you to keep always?’

She turns to Polly and smiles as if she knows the answer already.

Polly looks into her teacher’s eyes and suddenly she knows what it is, too.