‘Excuse me,’ she said.

Neither of them turned.

‘Excuse me?’ said Bea again. ‘Hi.’

‘Fuck off,’ said the girl, still not turning.

Bea couldn’t see them clearly. The air smelled musty and the street was very loud.

‘It’s all right!’ called the woman at the counter, but she sounded frightened.

Bea looked at the passers-by on the pavement, hurrying, unnoticing, then she put her shoulder against the door and pushed it hard, and squeezed through the gap into the shop. The door closed behind her.

‘Fuck off,’ said the girl, turning round to face Bea. She was holding a knife.

It wasn’t a fighting knife, it looked like a kitchen knife, and she didn’t hold it out, just gripped it in her hand. Behind her, the woman opened her eyes wide in a mute distress signal.

‘What do you want?’ said the girl.

‘Are you all right?’ Bea asked.

The girl was tall, with long legs in skinny jeans and trainers that seemed too big for the rest of her.

‘What are you doing? Go away,’ she said. Bea thought she looked high. She was speedy and scattered.

The woman behind the counter walked backwards, silently, disappearing into the darkness of a doorway. Bea smiled at the girl to keep her attention. She had been crying. Her make-up was smudged and her skin was very white. She didn’t look as if she knew she was holding a knife.

‘I just wanted to ask how much that bag in the window is,’ said Bea. ‘The red one?’

The girl was confused, eyes darting from one place to another. She wiped her face and tucked her hair behind her ear.

‘Sorry,’ said Bea. ‘You don’t work here, do you?’

‘I had to get out,’ said the girl. ‘Are you judging me? You don’t even know me.’

‘Can you put that away?’ said Bea. ‘It’s scary. Do you mind? Can you put it in your bag?’

The girl looked down at the knife in her hand. She jabbed it at the empty air, and laughed. ‘I’m sorry,’ she said. ‘It’s not funny.’

Still holding onto the pushchair, she knelt down and shoved the kitchen knife in the clutter of her gaping bag. Bea could see the baby’s feet sticking out but she couldn’t see the rest of its body. She thought the woman must have called the police. She walked towards the girl.

‘I’m on my lunch hour,’ she said. ‘I was just passing. Are you going to be OK?’

‘What?’ said the girl.

‘Are you OK?’

‘What’s your name?’ said the girl.

‘Bea,’ said Bea. ‘What’s yours?’

‘Emma,’ said the girl, ‘and this is Thomas.’ She nodded towards the baby.

‘Like the Tank Engine,’ said Bea.

The girl smiled. ‘Yes.’

Bea took a few more steps, and leaned over to look into the pushchair. The baby was very young, very small. He was asleep. His hands were curled up by his head, his tiny fingers were as clean as freshly shelled peas. Then they heard sirens. Emma tensed and stared towards the sound. Then blue light flashed onto the walls as the police cars pulled up at the kerb. Two cars and a van. Doors opened and police got out in what looked like a crowd, dark, heavy clothes, pulling on caps and jackets, talking on their radios.