Catherine was perfectly calm as she made this statement, but only a dullard could have missed the steel in her voice.

Declan sighed. ‘Very well, Catherine. If Captain Vigny permits it.’

Vigny’s only answer was a Gallic shrug that said, Permit it? I pity the man who tries to stand in this woman’s way.

Catherine smiled.

‘Very well, it is settled. Shall we cast off?’

Le Soleil loosed its anchors shortly before three that afternoon, quickly climbing to a height of a few hundred feet.

‘We are in heaven,’ sighed Catherine, clutching her husband’s hand tightly.

The young couple looked upwards into the belly of the balloon itself. The silk was set shimmering by the breeze and sparkling by the sun. Golden waves billowed across its surface, rumbling like distant thunder.

Below them the Trocadéro gardens were emerald lakes, with Lady Liberty’s head breaching the surface like a Titan of legend.

Vigny fed a small steam engine, sending power to the twin propellers. Fortunately, the prevailing wind snatched the smoke away from the basket.

‘Impressive, non?’ shouted the Frenchman above the engine’s racket. ‘How many are you thinking of ordering?’

Declan pretended not to be impressed. ‘Perhaps none. I don’t know if those little propellers would have any effect against an ocean wind.’

Vigny was about to argue the merits of his steam-powered dirigible when a sharp flat crack echoed across the skies. It was a noise familiar to both soldiers.

‘Gunshot,’ said Vigny, peering towards the ground.

‘Rifle,’ said Declan Broekhart grimly. As captain of the Saltee Sharpshooters he knew the sound well. ‘Long range. Maybe a Sharps. See, there.’

A plume of grey-blue smoke rose into the sky from the western border of the gardens.

‘Gun smoke,’ noted Vigny. ‘One cannot help wondering who the target might be.’