Polly sits up in bed with a bowl of lizard broth in her lap, the afternoon sunlight slanting through her window. She takes a couple of obedient spoonfuls while her mother hovers, plumping up pillows and picking up shoes and socks from the floor.

But as soon as her mother leaves the room, Polly puts the bowl down on the carpet where she knows Gumpy will gratefully demolish the oily grey soup.

Polly gazes out the window towards the tree at the end of the garden. Her stomach churns with worry and lizard broth. She needs to get a message to Buster to see if he is OK. She hasn’t been able to stop worrying about him all afternoon.

The image of Buster in the gallery keeps flashing into her mind. The look of hurt and surprise when Polly pretended not to know him.

But this is what we always do! she thinks, trying to forgive herself for her meanness. He knows that nobody must know we are friends. A flicker of annoyance at his carelessness sparks through her. It’s not all my fault!

Polly hears Winifred downstairs, home from school. She is chatting excitedly to their mother in the kitchen, though Polly can’t make out what they are saying.

Then Winifred’s footsteps bound up the stairs, and her sister bursts into the room.

‘Aster at school says you did a massive spell at the gallery today! Is that true?’

She swoops over and sits on Polly’s bed, her eyes lit with glee. It’s rare for Polly to see Winifred look anything other than bored or annoyed, and she can’t help feeling a thrill at her sister’s sudden interest in her.

‘Everyone’s talking about it. What was it like, doing the spell?’

‘Well,’ says Polly, ‘it just kind of happened. I felt really hot. And there was a flash of light. It was like electricity going through me. It was pretty scary, actually.’

She glances at her sister and is pleased to see she’s impressed.

‘Mum says there were monsters in the gallery. She says they were menacing Malorie Halloway, and you did the spell to scare them off.’

‘Well, it wasn’t exactly like that,’ Polly says.

‘Monsters are awful,’ Winifred shudders. ‘They’re smelly and noisy and they break things and hurt people. I hate them!’

‘That’s not true,’ Polly says. ‘They’re not all like that.’

Winifred turns to Polly, a cruel smile sliding across her face. ‘Yes, they are,’ she says, taunting. ‘All of them. Mum says. So do all my friends at school.’

Polly frowns. She knows exactly where this is going. Winifred is always looking for an opportunity to bring up Buster.

‘You used to play with Buster, too,’ Polly says crossly.

Winifred sneers. ‘Polly, he’s a monster. And he’s a weird monster at that. You two suit each other. You’re both weird.’

‘Stop being so mean!’ Polly says, frowning.

‘Stop being so mean!’ Winifred teases. ‘It’s not my fault you’re weird. It’s just a fact.’

‘You’re horrible,’ Polly says, feeling her cheeks stinging pink. ‘Get out of my room!’

‘Why should I?’ Winifred says, picking at her flaking nail polish.

‘Because it’s my room!’ Polly yells.

‘Polly! Winifred!’ their mother calls out.

‘Mum told me to check up on you,’ Winifred says, not budging. ‘I’m just doing what I was told to do.’

‘I hate you,’ Polly seethes. ‘You’re the worst sister ever!’

But then, as she watches, Polly sees Winifred’s face crumple. Her sister bows her head into her hands and begins to make deep sobbing sounds.

‘Oh, Winny. I’m sorry!’ Polly says, clambering across the bedclothes to reach her sister. ‘I don’t really hate you. I didn’t mean it!’

And it’s true. When she was little, Polly loved her sister so desperately it hurt. All she really wants is for it to be like that again. When their dad was still alive and everything was right in the world.

She strokes Winifred’s glossy black hair. ‘Winny, I’m sorry. Don’t cry!’

Winifred jerks her head out of her hands and grins nastily at Polly. ‘Ha! Tricked you!’ she laughs. ‘You might not hate me, but I still hate you!’

And she jumps up from the bed, laughing loudly at her tremendous joke, and slams Polly’s door behind her.

Polly feels her heart bruised and heavy.