Julianne Quentin arrived home after dark to find a police car parked outside her front door. Her steps slowed. She hoped, as she approached, that they’d start the engine and drive away. But she saw them notice her, the way they sat up straighter as she walked towards them – they were here to see her. She’d knock on their window, ask if they needed her help with something. But before she could the door opened and two uniformed officers stepped out. It had been such a long time since she’d seen the police that they almost looked like they were in fancy dress. But at the same time she knew that they wouldn’t be here unless there was a reason.

‘Would you like to come in?’ she said, keeping her voice calm and authoritative, as she did in every situation she found herself in.

They nodded and thanked her – although they didn’t smile – and followed her into the house where she sat them down on the sofa, and took the single chair opposite.

‘There’s been an accident,’ they began. ‘I’m so sorry, Mrs Quentin. There’s been an accident on the Tube …’ And somehow it felt like she’d known what they were going to say, as though this had been coming, and she’d been waiting, rehearsing her side of the script. Except that she didn’t have any words.

As a young woman, Julianne had spent a long time thinking about what she wanted her life to be. There were ideas there years before she understood the practical realities of them. She loved flying – ever since she was too young to remember, according to her parents – and so she studied the subjects that could bring her closer to flight. She always knew she would work with aeroplanes, and she did.

She always knew she would have a family, too. Though, just as running down a hillside didn’t teach her much about the equations of motion, the idea of having a family and the way it was achieved seemed very far apart, when she was little. Perhaps it was the shock that made her determined to understand how everything worked as an adult. She got her PhD in eighteen months, a record for her department. She knew that knowledge meant power.