A Riddle in Bronze

felt like the entire house was swaying. I'd read hair-raising tales of earthquakes as a boy, but even though they were unheard of in this fair land I could think of no other reason for the violent movements.
Roberta wound the device with a small key protruding from one side, then set the smallest of the three pendulums in motion. She seemed oblivious to the commotion all round us, as furniture rattled and the very walls threatened to fall in. "What's causing this?" I shouted over the noise. "Was it something we did?"
"Please! Let me calibrate the detector."
I held my tongue even though I had a dozen more questions begging to be asked. Instead, I supported myself by gripping one upright of the four-poster bed, and then I watched Roberta at work. The second pendulum on the device was now in motion, moving in counterpoint to the first, and she adjusted the angle of the metronome before starting the third and largest pendulum. This one swung to one side, hesitated several seconds, then swept quickly to the opposite side. Along the way it disturbed the motion of the two smaller hands.
The floor trembled again, fiercely this time, and I heard a distant crash. I guessed one or more tiles had slipped from the roof to smash on the ground below, and I hoped nobody had been in their path. That gave me pause for thought, and I struggled to the window, using furniture to help with my balance. When I got there I looked out on the street, where I saw scenes of total chaos. People were running in every direction, trying to avoid the terrified horses that were bucking and rearing in the traces of their laden carts. Several large vehicles had overturned, and I saw gangs of men bearing the scattered cargo away while the drivers were occupied with the frightened beasts. I saw three or four huddled forms lying still in the middle of the road, whether struck by carts or crushed in the panic, I had no way of telling. Even as I watched, an urchin ran to one of the wounded and helped himself to the man's pocketbook, before fleeing down an alleyway. Moments later a pair of constables appeared on the scene, blowing their whistles before setting off in pursuit.
"It's about eighty feet below us!" called Roberta.
I turned to see her studying the metronome device, whose pendulums had all ceased moving.
Roberta gestured towards the window. "The source is somewhere between here and South Kensington."
I saw the worried look on her face, and I understood the reason. Her home, her father… South Kensington was precisely where they were located. I glanced to my right, where the bulk of the city was hidden behind rows of houses, and then at the nearby trap with its gleaming bronze cylinder. The device was still shaking, but whether it was the movement underfoot or the angry spirit I had no way of knowing. "This tremor… could it be connected to the phantasm?"
"How could it be? Nothing like this has ever happened before!" declared Roberta.
"Your father was possessed by a spirit earlier in the day," I said. "You told me that never happened before either. What if… what if there are far more powerful phantoms than you've encountered before?" I gestured at the trap. "What if these are merely supporting players, and the protagonist has yet to reveal itself?"
"Mr Jones, you have an overactive imagination," said Roberta, but for once her air of confidence had deserted her.
Then, without warning, the tremors died away. In the sudden silence I heard the frantic tick-tock of the metronome device, until Roberta stilled the pendulums. There were cries from the street still, but they were lessening now that the upheaval had ceased.
"Thank goodness that's over," said Roberta. "Would you help me with the equipment?"
It took a good half an hour to pack everything away, after which we tidied the room as best we could. Then, following a last look around, we shouldered our haversacks and headed downstairs.
– — Ω — –
We met Annie near the kitchens, where the cook was keeping up a non-stop monologue as she dealt with the aftermath of the tremors. There were several overturned pots and pans, and steaming liquid formed pools on the tiled floor. "What's the world coming to?" demanded the cook. "Shakes and quakes and convulsions like I've never seen, the Lord be my witness. A body can't even cook dinner without the walls come tumbling down around their ears. If you ask me…"
The maid led us out, and as we left the house the cook's stream of protests faded into the distance. We took the alley to the main road, where workmen were setting carts back on their wheels and helping to reload the cargo. The police constables I'd seen earlier were overseeing events, and calm of a sort had returned to the scene.
It was five minutes before we could hail a cab, but eventually we were on our way to the station, the haversacks at our feet. I could see the square bulge of the trap inside Roberta's bag, its victim still inside, and I wondered how the crowd would react if they knew what moved amongst them. Sheer panic, I suspected.
The hansom cab stopped outside the station, where we alighted and purchased our tickets. Then we took the stairs to the underground, boarding the cramped carriage as quickly as possible to avoid the thick haze, the noise and the smell. Before long we were under way, the train rattling and groaning as it navigated the tracks in the tunnel. The gaslights in the carriage cast hardly any light, and the thick smoke seeping through the windows dimmed the interior even further. I closed my eyes against the fumes, for just a moment, and let the day's events wash over me.
I was in the habit of writing a letter home to my parents once weekly, letters in which I disguised my true situation. Now, I