Not standard Morse — too easy to filter.

A modified numeric sequence based on structural telemetry standards for commercial high-rise construction, the notation system from my graduate work in architectural engineering. The numbers encoded three things: approximate depth below street level, compass bearing of the primary ventilation shaft, and the frequency signature of the subterranean infrastructure vibrating through the floor since I woke.

If anyone on the surface was monitoring deep-structural acoustic leakage — a long shot, but not impossible in a city where the MTA and ConEd ran continuous seismic monitoring — that anomaly would propagate upward through bedrock, through steel reinforcement, and register as a faint structured pulse somewhere in the grid.

A message in a bottle, tossed not into the ocean but into the bones of the city itself.

The crescendo built. My fingers flew across the keyboard, impact jarring through wrist joints, ache spreading through my forearms. Sweat prickled along my hairline.

I didn't look at the glass partition. Eyes locked on the empty music rack, face a mask of concentrated fury that Alistair would interpret as emotional catharsis — a prisoner releasing rage through the only outlet available.

The final chord crashed down like a door slamming shut. Strings rang, overtones shimmering, then decayed into a hum that seemed to come from the walls themselves — concrete vibrating at a sympathetic frequency, the entire room a resonating chamber.

Silence.

The monitoring lights pulsed once. Twice. The climate system exhaled a soft breath of filtered air.

Then, from the other side of the glass, a sound through the speakers. Slow. Rhythmic. Deliberate.

Clap. Clap. Clap.

Alistair's applause.

The glass cleared. He stood in the dim corridor, leaning against the beam with arms crossed, sleeves rolled to his elbows. His eyes fixed on me with an expression that tightened the skin on my neck — not anger, not mockery, but something far more dangerous.

Genuine fascination.

"Magnificent." His voice slid through the speakers, intimate, calibrated. "Such precision. Such unyielding defiance. Though I admit — I didn't take you for a classical romantic."

I stood slowly. Thighs aching where hard wood had pressed into muscle. I smoothed the linen shift and met his gaze.

My heart was hammering — not fear, but six minutes of sustained fortissimo. I locked my jaw and refused to let my breathing betray the exertion.

"Music is just math, Alistair." My voice level and clear. "And every puzzle has a solution. You just have to know how to count the beats."

His smile widened by a fraction — a dangerous increment that told me he was filing every word, every inflection into the obsessive archive he was building inside his head.

Good. Let him file. Let him think the performance was the message.

The real message was already traveling through the bedrock beneath our feet, riding the resonant frequency of the city's bones toward a surface he couldn't see.