The crawlspace was a tomb of forgotten dust and the skeletal remains of the Georgian era. It was so narrow that Mycroft's great bulk seemed to threaten the very structural integrity of the floorboards above us. I could hear the joists groaning under his weight, a sound that, to my heightened senses, seemed loud enough to alert the intruder currently pacing the floor of our sitting-room.
"Breathe shallowly, Watson," Holmes whispered. His voice was a mere vibration in the dark. "The soot here is rich in carbonized coal and arsenic from the old furnaces. One sneeze, and we are discovered."
We moved like specters through the subterranean gloom. My left shoulder, the site of that wretched Jezail bullet, throbbed with a dull, rhythmic ache that seemed to count the seconds of our escape. Every inch of forward progress was a battle against the claustrophobia that clawed at my chest. Above us, the heavy, measured tread of the intruder continued—seventeen steps to the window, seventeen steps back. It was a metronome of malice, a cadence that suggested the creature above was not searching, but waiting.
Finally, we reached the brickwork that marked the boundary of 223 Baker Street. Holmes felt along the mortar until his fingers found a loose header-stone. With a strength that always belied his gaunt frame, he levered it out, revealing a rusted iron grate that opened into the neighboring cellar.
We tumbled through, one by one, into a space that smelled of damp earth and rotting potatoes. 223 had been vacant for months, a fact for which I offered a silent prayer of thanks. Mycroft landed with a heavy thud, gasping for the oxygen that had been so cruelly thinned by the corrosive liquid above.
"That... was... singularly undignified," Mycroft wheezed, adjusting his disheveled cravat. Even in the face of death, the elder Holmes seemed primarily concerned with the breach of protocol.
"Dignity is a luxury of the living, Mycroft," Sherlock remarked. He was already at the coal-chute, peering up at the street level. "The fog has thickened. It is a 'pea-souper' of the first order. If we move now, we can reach the Marylebone telegraph office before the Sub-Committee realizes we have slipped through their fingers."
"The office will be watched," Mycroft warned.
"Naturally. But they will be watching for a party of three—one tall and thin, one stout, and one of military bearing. They will not be watching for a blind beggar, his simpleton son, and a distracted clergyman."
In the corner of the cellar, I saw a trunk of old theatrical costumes—remnants, no doubt, of the previous tenant, a failed actor of the Drury Lane. With the speed of a stage-magician, Holmes began to distribute garments. I found myself draped in a threadbare black cassock that smelled of mothballs, while Mycroft was forced into a tattered overcoat that barely met across his chest. Holmes himself disappeared into a ragged cloak, his face suddenly collapsing into the vacant, sagging lines of an old man whose wits had long since departed.
We emerged into the street not as the residents of 221B, but as three shadows among many. The fog was so dense that I could scarcely see my own hand before my face. It muffled the sounds of the city, turning the rattle of a distant hansom into a ghostly, disembodied echo. We walked in silence, Holmes leading us with an unerring sense of direction that seemed to bypass sight altogether.
The Marylebone telegraph office was a beacon of sickly yellow light in the gloom. Outside, a man leaned against a lamppost, his collar turned up. He appeared to be reading a newspaper, an impossible task in such light. As we passed, his eyes flickered toward us—cold, observant eyes that saw everything and revealed nothing.
"Keep walking, Father," Holmes whispered to me, his voice cracking with the perfect imitation of a simpleton's whine.
We entered the office. The telegraphist, a pale youth with ink-stained fingers, looked up with an expression of profound boredom.
"Message for Mr. Sigerson," Holmes wheezed, tapping a coin against the brass railing.
The youth shuffled through a stack of yellow slips. "Came through ten minutes ago from the Continental line. Vienna."
He handed the slip over. Mycroft leaned in, his heavy brow furrowed. Sherlock smoothed the paper on the counter, and I felt a cold shiver go down my spine as I read the transcript:
CLOCKMAKER FOUND VIENNA RINGSTRASSE STOP LOCKED ROOM STOP NO PHYSICAL TRAUMA STOP GEOMETRY CARVED IN FLOORBOARDS IDENTICAL TO SPECIMEN A STOP VARIABLE CANCELLED AT 10:14 PM STOP SOLUTION APPROACHES ASYMPTOTE STOP
"The clockmaker," Mycroft whispered. "Old Hans Meyer. He was the finest horologist in Europe. He designed the synchronization mechanisms for the Austro-Hungarian railway."
"And he was the 'Variable of Friction' for Vienna," Holmes said, his voice dropping its disguise. "Look at the timing, Mycroft. 10:14 PM. That is precisely the moment the courier died on our landing. The cancellations are simultaneous. It is not a sequence of murders; it is a coordinated strike across the continent."
"But why a clockmaker?" I asked. "What threat could a man of eighty, who spends his days among gears and springs, pose to the British Empire?"
"Meyer didn't just make clocks, Watson," Holmes said, his eyes burning with a dark fire. "He studied the mathematics of resonance. He understood how small, periodic vibrations can, over time, bring down the most massive of structures. If one knows where to tap a bridge, a single hammer can collapse the span."
He turned the telegram over. On the back, written in the same precise, non-Euclidean script we had seen on the parchment, was a new string of symbols:
$$\int \frac{Regis}{\Delta} dt = \Omega$$
"The integral of the Crown over time," Mycroft translated, his voice trembling. "They are calculating the end of the Monarchy. They believe that by removing Meyer and the courier, they can change the value of $\Omega$—the final outcome."
"They are not just predicting the future, Mycroft," Sherlock said, grabbing my arm with a grip that was painfully tight. "They are editing it. They are pruning the human race as though it were a hedge, cutting away any branch that might grow in an inconvenient direction."
Suddenly, the telegraphist let out a muffled gasp. I looked up to see the man from the lamppost standing in the doorway. He was no longer holding a newspaper. In his hand was a long, slender cylinder of blackened steel—the same kind of clinical instrument that had ended the life of the courier.
"The telegram, if you please," the man said. His voice was devoid of emotion, as flat and cold as a sheet of ice. "It is a matter of state security."
"On whose authority?" Mycroft demanded, drawing himself up to his full, imposing height.
"The authority of the Equation," the man replied.
He raised the cylinder. I saw the glint of a needle at its tip. Mycroft stepped forward, perhaps intending to use his bulk as a shield, but Holmes was quicker. He seized a heavy glass inkwell from the counter and hurled it with unerring aim. It shattered against the man's forehead, a spray of black ink exploding across his face.
"Run, Watson!" Holmes shouted.
We dived through the side door, into the labyrinth of the railway yard. Behind us, I heard the hiss of compressed air—the sound of the needle being fired—and then a sharp, metallic clang as it struck the iron doorframe just inches from Mycroft's head.
We scrambled over a series of fog-slicked tracks, the smell of coal-smoke and steam hot in our faces. My breath came in ragged gasps, and the pain in my shoulder had shifted from a dull throb to a searing heat. We ducked behind the massive, pulsing flank of a stationary locomotive, the Orion, which was huffing rhythmically as it prepared for the midnight run.
"We cannot go back to Baker Street," Holmes said, pressing his back against the vibrating iron of the engine. "We are officially 'Variable Friction' ourselves now."
"Where then?" I asked, checking the cylinders of my Webley.
"We go to the source," Holmes said. He looked at the telegram again, his eyes narrowing. "The clockmaker was murdered at 10:14. The next cancellation is scheduled for tomorrow night in Rome. The Cardinal of San Giovanni. We must reach him before the Equation does."
"Sherlock, the ports will be closed!" Mycroft hissed.
"Not to a dead man, Mycroft. We shall take the express to Dover, but we shall not be on the passenger list."
At that moment, the locomotive let out a deafening blast of its whistle, a scream that seemed to tear the very fog asunder. From the darkness of the tracks behind us, three more figures emerged, their blackened steel cylinders gleaming in the firelight of the engine's cab. They did not shout; they did not call for our surrender. They simply advanced in perfect, mathematical unison.
"On the cow-catcher, Watson! Now!"
Holmes leaped onto the moving frame of the engine just as the wheels began to churn. I grabbed Mycroft's hand, hauling him upward with a strength I did not know I possessed, even as a needle whistled past my ear and buried itself in the wooden sleepers of the track. As the Orion gathered speed, plunging into the black maw of the tunnel, I looked back to see the three assassins standing perfectly still on the platform, their eyes fixed upon us with the patient, terrifying certainty of a solved problem.