She paused to step over an open sewer. ‘Just because there isn’t a revolution doesn’t mean we don’t have to choose who we are.’

James didn’t reply. She shot a glance back at him and thought she caught a flicker of tension.

‘No,’ he said eventually as they were passing the muddy banks by the Hôtel de Ville where the Paris Commune held court. ‘You’re right. I suppose that’s why I’m here. I want to make sure Cam knows that I still choose her – it was rather decided for us, our families were friends and it seemed natural that we should marry. Everything has changed, of course, but I want to make sure she knows that when this blows over she still has a family. Somewhere to belong.’

Ada felt as if she’d been punched. She took a few moments to collect herself before she said, ‘Cam has a family. She has us. I think she’s happy.’

‘Ah, well. That’s Cam for you. You never can quite tell if she’s happy – or angry or sad or bored, or much of anything. She keeps it all closed up in her head because I don’t think she knows herself what would make her happy.’

‘And you do?’

He shrugged. ‘I’ve spent most of my life trying.’

Across the river, the Place de Grève was busy with people loitering, hoping for work in the farms or factories, or unloading wood, wheat, wine and hay from the boats gathered in the old port. A few young girls were dancing while a boy played the revolutionary anthem ‘Ça Ira’ on a fiddle, practising for the grand parade at the Festival of the Supreme Being.

They turned into side streets, Ada nursing a ball of hurt, as they weaved towards the bookshop she thought might have something useful.

She had another reason for going there, but she didn’t need to tell James about that.

Outside the bookshop, trestle tables had been set up with boxes of cheap chapbooks and old pamphlets curling at the corner stuffed in with prints and maps and other papers. It took some digging to find anything promising: a badly damaged copy of Turgot’s 1739 map of Paris, but the square showing the Faubourg Saint Martin was intact. The abbey was picked out in beautiful detail, each tree in the garden, each window and doorway. It was perfect.

Ada went inside to buy it. Passing the scientific shelves, she picked up a copy of Galvani’s Commentary on the Effect of Electricity on Muscular Motion. She hadn’t taken her copy when she left home, but she thought it would be useful to understand more about Olympe’s powers.

The owner was a short elderly man, perched among stacks of books like a crow watching for carrion. Bookselling was one of the few industries thriving under the Revolution, after the royal censor had been eliminated.