The corridor branched left and right. The cellars spread across most of the building, from the oubliettes where the poorest prisoners were dumped, to the old Merovingian palace and the catacombs of the Sainte-Chapelle. That was north from where they’d crashed. They could get out through the chapel. Probably.

‘This way!’

She pulled the boys left.

‘So what do we do now?’ asked Al as they dashed through passageways.

‘Cam knows what she’s doing,’ replied Ada. It made her feel sick to think of leaving without her, but she knew it would be what Camille wanted. ‘We need to get out. Not a bad thing if we cause a scene doing it.’

They turned down the last twist of corridor – into a dead end.

There was a locked door in front of them. Behind, the footsteps of the soldiers drew closer.

‘Somehow,’ said Al, ‘I don’t think that’s going to be a problem.’

Ada pulled a pin from her hair and kneeled to work on the lock.

‘Do you still remember how to do that?’ asked Al.

‘I’ve done it before when I’ve had to,’ replied Ada through gritted teeth. ‘I can do it again.’

‘What’s through there?’

‘I don’t know. Prisoners, probably.’

‘Well, that’s good. Let them all out and swamp the soldiers. That should be enough of a scene.’

A soldier came round the corner, musket in hand. But Guil was ready for him. He fired, hitting the soldier in the thigh. He crumpled with a yelp and fumbled with his musket. Guil lined up another shot, as another uniform appeared round the edge of the stone wall and hooked his hands under the fallen man’s armpits to haul him back to safety. Guil’s bullet snipped the wall above his head, sending a shower of fragments skittering down. Their bright white uniforms vanished and Guil fell back to reload. The white of his borrowed uniform trousers and waistcoat were smudged with dirt, and he’d loosened the red necktie.

‘Work faster, Ada.’

She ignored him, focusing on the minute movements of the pin against the tumblers in the lock. She had all but the last tumbler raised; the angle was difficult and her pin was too short to lift it fully. Her fingers were sweaty. She pressed up with the pin, forcing it against the tumbler. The pin slipped in her fingers and clinked onto the floor.

She swore.

‘Faster, but also accurately,’ hissed Al.

Ada wiped her hands on her dress and picked up the pin again. She could do this. She had the feel of the lock now. She just had to tune out Al’s twitching and the voices of the advancing soldiers and the smell of gunpowder burning her nose.

‘You’re not exactly doing anything to help.’

‘Cellar gun battles aren’t my forte. I’ll leave that to the petty criminals like you two.’