Finally a horn sounded from the marshes, a cheer went up from the dragoons, and the edge of the island turned red as the First Company of the Queen’s Own Black Torrent Guards emerged from the grass, all in a wide line, and began to advance over the flats at a trot.

Daniel looked at the Tor. It was square-floored, each face of the building something less than ten yards wide. Perhaps twenty yards’ altitude separated its gaptoothed parapet from its foundation-a pile of boulders atop a lens of greasy black stone that poked up through the bank. “Shive” was a primeval English word for knee-cap, and Daniel, who had sliced a patella or two from cadavers, could see how the rock had come by its name. Slime and barnacles coated the lower reaches and made it difficult to tell where the natural plinth left off and the man-made work began. The Tor had been built up out of bulky brown boulders probably prised from a quarry upriver, barged down at high tide, and rolled overboard. White mortar held it together. There was but a single door, which looked out onto a silted pool at the terminus of this long gouge that they were fitfully navigating. The threshold was an arm’s length above where the fur of wee crusty creatures and rank weeds gave way to bare, wave-washed stone. So that was where they had built a floor. From the situation of windows (if that was not too grand a term for them) higher up, Daniel estimated there was a wooden platform above, forming an upper storey, and above that a roof, on which lookouts and gunners might stand to look out over, or through, the woebegone parapet.

“Is there room here for so many horses, when the tide comes in?” Daniel asked.

“First you were worried they would not come at all-I could see it in your phizz-now you’re worried because they’re coming!” Barnes returned. “It is nonetheless a question that deserves an answer. We are dragoons, Doctor. The horses are mere vehicles. When the men are here, the beasts will be sent back straightaway-they’ll be back on the Isle of Grain half an hour from now.”

“I do beg your pardon, Colonel. As a wise man once told me, we are all scared.”

Barnes nodded gracefully. But he could sense a Newtonian glare boring into the other side of his head, so without delay he said to the sergeant, “Let us advance, and see if we draw fire from the Tor.”

“I did not understand that Sir Isaac Newton’s role was to draw fire,” Daniel shot back peevishly, then bit his tongue as even Isaac was smiling at Barnes’s jest. Annoyed now with everyone on the boat, including himself, Daniel snatched the blanket-ten pounds of greasy Qwghlmian wool-and settled it over his shoulders. It prickled him through his clothes like a heap of thistles, but it would eventually be warmer.

The longboat balked mulishly as it scraped its keel on the sandy bottom every few yards. Sergeant Bob became exasperated, then profane, to the point where Sir Isaac became visibly offended. Half of the dragoons divested themselves of their powder-horns and granadoes, and vaulted over the gunwales to land waist-deep in the channel. This lightened the boat’s load enough to get its keel out of the muck, and it enabled them to move it along by pushing on it with their shoulders, as if it were a gun-carriage mired in Flanders. “Take advantage of the shallow water,” Barnes said approvingly, “we’ll not have it much longer.” The colonel had mostly been keeping an eye on the parapet, clearly worried about snipers. Isaac’s gaze was fixed on the hooker, which was now rolling freely on the bank of the channel-the direction of the tide had reversed! The sergeant was attending to his men.

Daniel was the only one aware that the charge of the First Company from the Isle of Grain had come to a halt as soon as it had got started. Only a few yards beyond the cockle-belt, a few of the horses had gone down. The rest had halted, and the line of redcoats had split and spread into two wings, trying to probe around some obstacle. A pistol-shot tolled for a broken-legged horse. This got everyone’s attention. They heard, too, a distant thudding noise: an axe striking wood.

“Jack’s men drove pilings into the mud,” was Bob’s guess, “and stretched chains between ’em, to stop the horses. This they would’ve done in the highest and driest parts, where the best footing was to be had; which tells us that the flanks are now in a mire. Someone is trying to chop through a piling with an axe.”

“There are nails embedded in that piling, then, and his axe is already ruined,” announced Isaac absent-mindedly, without taking his eyes off the hooker.

“Sir Isaac has good ears,” Daniel explained to the incredulous Bob.

“Then he’d best plug them,” answered Bob and picked up a musket. A moment later the boat flinched from its recoil as he fired it into the air. He handed it to one of the dragoons, who set about furiously reloading.

“As long as you are wasting balls and powder, waste them on the parapet,” said the Colonel.

Within a few moments, several other muskets had been fired at the top of the tower, and a large glutinous mass of smoke had been set adrift on the calm evening air. No answering fire came back from Shive Tor. But the little fusillade had the effect Bob wanted: the dragoons off the Isle of Grain were dismounting, sending their horses back to dry land, and advancing on foot. Daniel was noticing that they now looked like dark motes against the gray sand. A few minutes ago their coats had been a proud red. The difference was not that they were all covered in greasy mud now (though they probably were), but that it was getting dark, and the colors were draining from everything. The evening star had come out, very bright, near the Tor.

A colossal thud came out of the far west. It was impressive enough to divert Isaac’s concentration from the hooker. “What was that?” he demanded-the first voice to violate the stillness that had descended upon all.

“A lot of powder was touched off at once,” said Colonel Barnes. “On a field of battle, it would signify a dreadful accident. Here, I guess it was the bridge over Yantlet Creek being demolished by a mine.”

“Why did you mine the bridge, Colonel?”

“I didn’t.”

Isaac was gobsmacked. “Then-who did!?”

“Now you ask me to speculate, Sir Isaac,” Barnes said coldly.

“But you have men posted at that bridge,” Isaac said.

“Or had, sir.”

“How could it have been mined, when it was under guard?”

“Again, speculation: it was mined in advance, the mine concealed from view,” Barnes said.

“Then, pray tell, who put fire to the fuse?”

“I’ve no idea.”

“No man was needed to put fire to it,” Daniel said.

“Then how was it lit?” Barnes demanded.

“The same way as that was,” Daniel answered, and shrugged an arm free of the blanket to point at the Tor.

Moments earlier he had seen a blue spark in his peripheral vision, and mistaken it for the evening star coming out near Shive Tor. But by now it had become brighter than any heavenly body save the Sun, brighter by far than any Comet. And it was not in the sky, but in one of those small irregular windows in the wall of the Tor.

Everyone was now looking at it, though it was growing brilliant enough to burn the eyes. Only Daniel and Isaac knew what it was.

“Phosphorus is burning inside the Tor,” Isaac remarked, more fascinated than alarmed.

“Then someone must be in there,” said Bob reaching for a musket.

“No,” Daniel said. “It was lit by an Infernal Device.”

The door of the Tor swung inward, shouldered out of the way by a waxing draught. The archway was a gem of yellow light. A small mountain of split and dried cord-wood had been piled on the floor, and had now been set a-blaze. Sparks had begun to fountain up into the sky, jetting through orifices that had been hacked through the upper floor and the roof.

“It is an admirable piece of work,” said Sir Isaac Newton, flatly and with no trace of rancor. “The rising tide obliges all to run inward to the Tor. But packed as it is with excellent fuel, this will soon become a furnace, and anyone near it will be roasted like a suckling pig. It truly is a choice between the devil and the deep blue sea.”