The sun had found a rift in the high clouds and illuminated veils of steam rising from the sweaty coats of their horses. “They’ll never catch him,” Eliza demurred, “in this wind he can out-sail them with ease.”

“Perhaps the Prince will take notice of that!” Fatio said, startled by a ragged volley of cannon-fire.

“He’ll only assume it is a salute, for some ship approaching the harbor.”

“What can we do, then?”

“Follow orders. Leave,” Eliza said.

“Then pray tell why are you dismounting?”

“Fatio, you are a gentleman,” Eliza called over her shoulder, kicking off the rabbit-pelts and stepping barefoot across the sand towards the other sailer. “You grew up near Lake Geneva. Do you know how to sail?”

“Mademoiselle,” said Fatio, dismounting, “on a rig of this plan I can out-sail a Dutchman. I want only one thing.”

“Name it.”

“The craft will heel over. The sail will spill wind and I will lose speed. Unless I had someone small, nimble, tenacious, and very brave, to lean out of the vehicle on the windward side, and act as a counterweight.”

“Let us go and defend the Defender then,” Eliza said, climbing aboard.

THEY COULD NOT POSSIBLY BEmoving as fast as it seemed, or so Eliza told herself until they caught up with the squadron of Blue Guards. With a twitch of the tiller Fatio could have veered round them as if they were standing still. Instead he let out the main-sheet and spilled a huge dollop of air, causing the sailer to drop to what felt like a slow walking pace-and yet they were staying abreast of the galloping Guards. The sailer dropped back onto all three wheels and Eliza, leaning way out on what had been the high side, nearly planted her head in the sand. Fortunately she was gripping with both hands a line that Fatio had hitched round the mast, and by pulling hard on this she was able to draw herself up faster than the zooming sand could lunge at her. And now she had a few moments to wipe spray and grit out of her face, and to tie her hair into a sodden knot that lay cold and rough against her neck. Fatio had got the attention of some of the Blue Guards by gesticulating and shouting in a hotchpotch of languages. Something came flying towards them, tumbling end-over-end, plopped into the mainsail, and slid down the curved canvas into Fatio’s lap: a musket. Then another, flung by a different Guard, whirled just over their heads and embedded itself barrel-first in the sand, surf swirling around its stock, and fell away aft. Now a pistol came flying toward them and Eliza, finally ready, was able to reach up and slap it out of the air with one hand.

Instantly Fatio hauled in on the sheet and the sailer hurled itself forward. He got in front of the foremost of the Guards and then veered up away from the surf onto drier and firmer sand. Eliza had had time to shove the pistol into her coat-sash now, and to get that rope wrapped securely round her hands; Fatio hauled the sheet in recklessly, and the sailer bit so fiercely into the wind that it nearly capsized. One of its wheels was spinning in the air, flinging sand and water at Eliza, who clambered over its rim, planted both of her bare feet on the end of the axle, and let the rope slither through her numb hands until she was leaning back almost horizontally and gazing (when she could see anything) at the undercarriage of the sand-sailer.

It occurred to her to wonder whether they were now traveling faster than any human beings had ever gone. For a minute she fancied it was so-then the Natural Philosopher in her weighed in with the observation that ice-boats had less friction to contend with and probably went even faster.

Then why was she so exhilarated? Because despite the cold and the danger and the uncertainty of what they might find at the end of the journey, she had a kind of freedom here, a wildness she had not known since her Vagabond days with Jack. All the cares and intrigues of Versailles were forgotten.

Craning her neck around, she was able to look out to sea. There was the normal clutter of coastal traffic, but mostly these vessels had triangular sails. The square-rigged jacht of the duc d’Arcachon should be conspicuous. Indeed, she thought she could see a square-rigger standing off several leagues from shore, a short distance to the north-that must be Meteore! The longboat would have come in at dawn and been hauled up on the beach so that the Prince would not notice it until too late.

Fatio had been raving for some minutes about the Bernoullis-Swiss mathematicians, therefore friends and colleagues of his. “Sail-makers of a hundred years ago phant’sied that sails worked as literal wind-bags, which is why ships in old pictures all have a big-bellied appearance that is very odd to our modern eyes, as if they need to be taken in… now we have learned that sails develop force by virtue of air-currents to either side, shaping, and shaped by, the curve of the canvas… but we understand not the particulars… the Bernoullis are making this their field of specialization… soon we’ll be able to use my calculus to loft sails according to rational principles…”

“ Yourcalculus!?”

“Yes… and it will enable us to attain speeds even… better… than… this!”

“I see him!” Eliza shouted.

Fatio’s view ahead was blocked by sail and rigging, but Eliza was in the clear, and she could see the top of William’s mast protruding above a low hummock of sand and beach-scrub. The Prince’s sailer was heeled over, but not so much as theirs, since he lacked a human counter-weight. He was perhaps half a mile ahead. Halfway between them, but coming up on them rapidly, was the said hummock, which (Eliza realized) was just the sort of visual obstacle behind which the dragoons would want to set up their ambuscade. And indeed she could see the mast of William’s sailer swinging up to vertical as he faltered and lost speed…

“It is happening now,” she shouted.

“Would you like me to stop and let you off, mademoiselle, or-”

“Don’t be foolish.”

“Very well!” Fatio now steered the sailer in a slashing arc around the end of the hummock. In that moment a mile of open beach was revealed to them.

Straight ahead and alarmingly close was a longboat, still cluttered with branches that had been laid over it as camouflage. This had just been dragged out of a hiding place on the north face of the hummock and was now being hauled and shoved down toward the water by half a dozen hefty French dragoons. At the moment its keel was slicing directly across the tracks that had been laid in the sand by William’s sailer a few seconds ago. It was cutting off the Prince’s line of retreat-and it barred Eliza and Fatio’s advance. Fatio jerked on the tiller and steered up-slope, round behind the boat. Eliza could only hold her rope. She clenched her teeth so that she would not bite off her tongue, and kept her eyes closed through a series of jolts. The wheels that were on the ground plunged across the furrow that had been cut by the longboat’s keel, and the one that was in the air smashed into the head of a startled dragoon and felled him like a statue.

The trim of the sails and balance of the vehicle were now all awry, and there was some veering and bouncing as Fatio brought matters in hand again. Sheer speed was not as important as it had been, and so Eliza put her whole weight on the hand-rope, raised her knees, and swung inwards far enough to plant her feet near the mast of the sailer. Fatio settled into a slower pace. They both looked up the beach.

A bow-shot ahead of them, another contingent of half a dozen dragoons were running in pursuit of the Prince of Orange’s sand-sailer. This had come to a stop before a barrier consisting of a chain stretched along a row of pilings that the Frenchmen had apparently pounded into the sand. The ambushers all had their backs to Eliza and Fatio, and their attention fixed upon the Prince, who had clambered out of his sailer and turned round to face the attackers.