In any case-without solving the eternal mystery of why Isaac did what he did-he spied the tangents paper on the far corner of the table, and stepped forward to reach for it.

The place was suffused with odd sounds, mostly the seething and hissing of diverse fuels burning in the furnaces, and the endless popping and ticking of the wooden wall panels. Another sound, faint and furtive, had reached Daniel’s ears from time to time, but that surly porter who bestrides the gate of the conscious mind, spurning most of what is brought in by the senses and admitting only perceptions of Import or Quality, had construed this as a mouse sapping and mining the wall, and shouldered it aside. Now, though, it did come to Daniel’s notice, for it grew louder: more rat than mouse. Isaac’s tangents paper was in his hand, but he stood still for a few moments, trying to work out where this rat was busy, so that he could come back in daylight and investigate. The sound was resonating in a partition separating this room from the big laboratory with the furnaces, which was not of regular shape, but had several pop-outs and alcoves, built, by men who’d long since passed away, for heaven only knew what reasons: perhaps to encase a chimney here, or add a bit of pantry space there. Daniel had a good idea of what lay on the opposite side of that wall that was making the grinding noises: it was a little sideboard, set into an alcove in the corner of the laboratory, probably used once by servants when that room had been a dining-hall. Nowadays, Isaac used the cabinets below it to store Alchemical supplies. The counter was stocked with mortars, pestles, amp;c. For certain of the things Isaac worked with had a marked yearning to burst into flame, and so he was at pains to store them in that particular alcove, as far as possible from the furnaces.

Daniel walked as quietly as he could back into the laboratory. He set the tangents paper down on a table and then picked up an iron bar that was lying next to a furnace door for use as a poker. There was more than one way to get rid of rats; but sometimes the best approach was the simplest, viz. ambush and bludgeon. He stalked down an aisle between furnaces, wiggling the poker in his hand. The alcove had been partitioned from the rest of the room by a free-standing screen such as ladies were wont to dress behind, consisting of fabric (now shabby) pleated and hung on a light wooden frame. This was to stop flying sparks, and to shield Isaac’s fragile scales and fine powders from gusts of wind coming through open windows or down chimneys.

He faltered, for the gnawing had stopped, as if the rat sensed the approach of a predator. But then it started up again, very loud, and Daniel strode forward, stretched one toe out ahead of him, and kicked the screen out of the way. His poker-hand was drawn back behind his head, poised to ring down a death-blow, and the candle was thrust out before him to find and dazzle the rat, which he guessed would be out on the counter.

Instead he found himself sharing a confined space with another man. Daniel was so astonished that he froze, and sprang several inches into the air, at the same instant, if such a combination were possible, and dropped the poker, and fumbled the candle. He had nearly shoved the flame right into the face of this other chap: Roger Comstock. Roger had been working in the dark with a mortar and pestle and so the sudden appearance of this flame in his face not only startled him half out of his wits, but blinded him as well. And on the heels of those emotions came terror. He dropped what he had been working on: a mortar, containing some dark gray powder, which he had been pouring into a cloth bag at the instant Daniel surprised him. Indeed drop did not do justice to Roger’s treatment of these two items; gravity was not nearly quick enough. He thrust them away, and at the same time flung himself backwards.

Daniel watched the flame of his candle grow to the size of a bull’s head, enveloping his hand and arm as far as the elbow. He dropped it. The floor was carpeted with flame that leapt up in a great FOOM and disappeared, leaving the place perfectly dark. Not that all flames had gone, for Daniel could still hear them crackling; the darkness was because of dense smoke filling the whole room. Daniel inhaled some and wished he hadn’t. This was gunpowder that Roger had been playing with.

Roger was out of the house in five heartbeats, notwithstanding that he did it on his hands and knees. Daniel crawled out after him and stood outside the door long enough to purge his lungs with several deep draughts of fresh air.

Roger had already scuttled across the garden and banged out the gate. Daniel went over to pull it closed, looking out first into the way. Some yards down, a couple of porters, shadowed under the vault of the Great Gate, regarded him with only moderate curiosity. It was expected that strange lights and noises would emanate from the residence of the Lucasian Professor of Mathematics. For shadowy figures to flee the building with smoke coming out of their clothes was only a little remarkable. Failing to close the garden gate was an egregious lapse; but Daniel saw to it.

Then, holding his breath, he ventured back in. He found the windows by grope and hauled them open. The flames had caught and spread in the fabric of the toppled screen, but gone no farther, owing to that Isaac suffered very little that was combustible to abide in the furnace-room. Daniel stomped out a few glowing edges.

In a more genteel setting, the smoke would have been accounted as a kind of damage to all the contents of the room that had been darkened and made noisome by it; but in a place such as this, it was nothing.

What had occurred was not an explosion-for the gunpowder, fortunately, had not been confined-but a very rapid burning. The screen was wrecked. The cabinetry in the alcove was blackened. A scale had been blown off the counter and was probably ruined. The mortar that Roger had dropped lay in fat shards at the epicenter of the black burst, making Daniel think of the cannon that had exploded at the “Siege of Maestricht,” and other such disasters he had heard about lately aboard ships of the Royal Navy. Surrounding it were burnt scraps of linen-the bag into which Roger had been decocting the gunpowder when Daniel had set fire to it. It was, in other words, the least possible amount of devastation that could possibly result from deflagration of a sack of gunpowder inside the house. That said, this corner of the laboratory was a shambles, and would have to be cleaned up-a task that would fall to Roger anyway. Unless, as seemed likely, Isaac fired him.

One would think that being blown up would throw one’s evening’s schedule all awry. But all of this had passed very quickly, and there was no reason Daniel could not accomplish the errand that had brought him here. Indeed, the grave problems that had so burdened him on his walk over here were quite forgotten now, and would appear to be perfectly trivial seen against the stunning adventure of the last few minutes. His hand and, to a lesser degree, his face, were raw and red from flash-burns, and he suspected he might have to do without eyebrows for a few weeks. A quick change of robes and a wash were very much in order; no difficulty, as he lived upstairs.

But having done those, Daniel picked up the tangents paper, shook off the black grit that re-punctuated it, and headed out the door. This was no more than a tenth of everything Isaac had accomplished with fluxions, but it was at least a shred of evidence-better than nothing-and sufficient to keep most Fellows of the Royal Society in bed with headaches for weeks. The night overhead was clear, the view excellent, the mysteries of the Universe all spread out above Trinity College. But Daniel lowered his sights and plodded toward the cone of steamy light where everyone was waiting.