The audio analyst's name was Peva Moss, and she worked out of a legitimate workspace in one of Tier Four's acoustic engineering sub-offices with a degree of deliberate normality that Kael found professionally admirable. The legitimate work was real — she had been assigned to a three-year maintenance project analyzing the resonance signature of the Spire's structural supports, which was the kind of unglamorous infrastructure work that no one paid much attention to and which consequently gave her access to some of the most sensitive audio analysis equipment in the Lower Tiers without anyone finding the access unusual.
The side work occupied a corner of the same space, in the two hours between the official workday's end and the facility's overnight lock protocol. Joss sat on a component shelf and watched while Kael handed over the chip.
Peva was thirty, with the focused economy of someone who had spent years treating every measurement as significant. She ran the chip through a reader first, cataloguing its basic parameters. Then she pulled the audio file and ran it through a spectral analysis program that Kael didn't recognize and couldn't afford.
"Standard consumer recording," she said, scanning the output. "Eleven-year-old format, captured on a portable device, secondary compression artifacts consistent with multiple format conversions over the life of the file." She scrolled. "The main content is a live performance — Resonance-element output present, Rhythmist signature, peak amplitude consistent with a Tier Eight performance venue." She kept scrolling. "Then silence from forty-three twelve onward."
"Keep going," Kael said.
She did. The spectral display showed the silence as a flat line — and then, at a frequency range below the standard consumer reproduction threshold, a cluster of data that the display flagged in yellow.
"There you are," Peva said softly.
She expanded the flagged section. The low-frequency cluster resolved into something structured — not noise, not artifact, but pattern. Four beats, as Kael had heard them, but with more information now visible. The beats had a specific signature: a Rhythmist's signature, the particular resonance fingerprint of a specific user's power output, the same way a voice had timbre.
"This was placed deliberately," Peva said. "Embedded in a sub-threshold frequency range using a high-precision discharge technique. Whoever put this here used a professional-grade resonance cell at very low output, targeted specifically at the frequency range below consumer playback." She turned to look at Kael. "This isn't a recording artifact. This is a message."
The word sat in the workspace.
"Can you decode what the pattern means?" Kael asked.
"The pattern itself is four beats in a specific rhythmic sequence. I can give you the precise timing and frequency values, but whether that translates to anything meaningful is beyond signal analysis." She looked at the display. "This looks like notation. Like a rhythmic cipher. The meaning would depend on a key I don't have."
"Can you extract it cleanly?"
"I can give you a clean isolated version of the pattern, yes. Full frequency data, precise timing values, amplitude profile." She did something with the interface. A secondary chip materialized from the output port. "That's your extract. The original file is unchanged."
Kael picked up both chips. He looked at the spectral display — the yellow cluster, the structured pattern that had been sitting in forty-three minutes and twelve seconds of his life for eleven years without him hearing it.
"Who's the Rhythmist signature?" he asked.
Peva looked at the display for a moment. She had the expression of someone running a comparison against a known database. "I can't say for certain. The output level is extremely low and the precision is unusual — most Rhythmists aren't trained to this level of discrete control at minimum output." She paused. "But the signature profile is consistent with archival recordings I've worked with from the Resonance Academy performance archive." Another pause. "Specifically, it's consistent with a performer whose archive was restricted about eleven years ago."
The workspace was quiet.
"Seren," Kael said.
Peva looked at him. She had the expression of someone deciding how much to say. "I've said what the analysis shows," she said carefully. "Signature consistency. Not identity."
"Of course."
She held his gaze for a moment. "The concert where that recording was made was Seren's last public performance before he disappeared. Whatever is in that file was put there by whoever was performing that night." She turned back to her display. "Joss told me you've had this for eleven years."
"Since I was six."
"You were at the concert?"
"I watched it on a shelter wall-screen. Someone made the recording there."
Peva was quiet for a moment. She was thinking about something, he could see it in the quality of her attention. "That shelter," she said. "On Three?"
"Tier Three southeast."
"The Harrow block residency?"
He looked at her. "How do you know the name?"
"I don't know it," she said. "It came up in a project I was working on last year. Infrastructure history, nothing sensitive. The Harrow block was built in a rush twenty years ago — emergency residential, post-industrial displacement, the usual Lower Tier story." She paused. "The project wasn't the building. It was the acoustic profile of the structural section it was built in. The resonance characteristics of the support column at that section of Three are unusual. The frequency range that column resonates at is — specific." She looked at the spectral display. "It's the same range as the embedded signal in your recording."
Kael stared at her.
"I'm not saying anything," Peva said. "I'm noting a coincidence."
"That's a very significant coincidence."
"Yes." She shut down the analysis display. "I've done the work I was asked to do. The extract is clean, the data is yours, my involvement in this is complete." She looked at him with the flat directness of someone closing a transaction. "Whatever you do with it, I wasn't here."
Kael and Joss left the facility ten minutes later, walking in the direction of the transit platform in a silence that lasted until they were out of the building and three corners away.
"The shelter column," Joss said.
"I know."
"That's not a coincidence."
"No."
She was quiet for a moment. "Someone put a message in a recording that would only be heard on equipment with a specific frequency range. And that message was in the same frequency range as the structural resonance at the building where the recording ended up." She worked through it. "Which means whoever embedded the message knew where the recording was going."
"Or knew where the person carrying it would end up."
Joss stopped walking. She looked at him.
"I was six," Kael said. "I don't know how I got that chip. The staff member who recorded the concert — I never knew her name. She gave it to me and then she left the shelter system, I don't know where." He held the chip in his hand. "Someone put a message in a recording and arranged for a six-year-old to carry it to a building that could theoretically play it back. And then the six-year-old grew up and got a room's audio system good enough to hear it."
"After eleven years."
"After eleven years."
They both looked at the chip.
"You need to figure out what the rhythm pattern means," Joss said finally.
"Yes."
"And you can't tell anyone else about this."
"I know."
She looked at him with an expression he recognized — the one she wore when she was weighing something that she didn't want to weigh, when the calculation was coming out to an answer she wasn't sure she trusted. "I'll help," she said. "Obviously. But Kael — someone set this up a long time ago. Before you were a fighter. Before you were anything except a child in a shelter." She paused. "Whatever this is, it was planned around you specifically. Which means someone has been watching you, or at least watching for you, for eleven years."
"Or they set it up and left it and trusted that the right person would find it eventually."
"And the right person just happened to be you."
He put the chip back in his pocket. "I don't know if I'm the right person," he said. "I just know I'm the person who has it."
They walked on. Tier Four's ambient noise came back in around them — the machinery, the transit sounds, the low constant hum of a city going about its business without any awareness of the small thing that had just shifted in a corner of it.
Kael kept his hand in his pocket, fingers around the chip, feeling the familiar weight of it. The same weight it had always been. But different now.