Sable showed up on day six.
Riven had expected her sooner, honestly. Six days of brief messages — I'm okay, I'm safe, I'll explain — was at the absolute outer limit of what Sable would tolerate before taking action. She arrived at the safe house at eleven in the morning with both hands full of breakfast food and the specific expression she wore when she'd decided to be calm about something she was actually furious about.
She looked at Theron. He looked at her.
"You have Riven," she said. "Tell her Sable is here."
"She's training."
"Then interrupt the training."
Theron turned slightly. "She's not available—"
"I have," said Sable, very precisely, "been running the biometric anomaly data from that club night through the university's spectral analysis system for six days. I have results." She held up the breakfast. "I also have food. So."
A silence.
Theron stepped aside.
⁂
The data Sable had pulled was not what Riven had expected.
She'd run the spectral signatures of the Hollow's physical dissolution against every biological and chemical database she had access to through the university's research systems, which — as a third-year graduate student in biochemistry — were significant. The dissolution event, the black smoke Riven had described, had left trace compounds in the air of the alley. Theron's ward-sensors had recorded them.
Sable had matched the compound signature.
"It's not organic," Sable said, spreading her printouts across the worktable with the focused urgency of someone presenting findings they know are important. "The dissolution byproduct is inorganic — it's entropic in a specific way that maps to theoretical models of energy-to-matter reversion. The Hollow, when they dissolve, are reverting to their base state. And their base state is—" She circled a number on one of the sheets. "Measurable. Recordable. Which means they have a consistent energetic signature we can track."
Riven looked at Theron.
He was reading the printouts with an expression she hadn't seen on him before. Not the assessment look or the training look or the carefully-managed professional look. This was simpler than all of those. This was someone reading something important.
"A passive detection system," he said.
"If you had the right sensor calibration," Sable said. "Which your existing ward-sensors almost have. They're reading the resonance, but they're not identifying the dissolution trace. If you tuned them to the specific spectral signature—" She tapped the number she'd circled. "You'd get a twelve-hour detection window. Any Hollow that dissolved in the area, you'd know about it."
"A twelve-hour window of movement history," Theron said.
"Which would give you a behavioral map." Sable looked at him with the expression she wore when she'd concluded someone was useful. "You're thinking about the eastern sector."
Theron looked up. "How do you know about the eastern sector?"
"Riven told me. Last night. On the phone."
He looked at Riven.
"She needed to know the relevant context," Riven said. "She's already in it whether we decided she was or not."
A pause.
"She's right," Sable said helpfully. "I was in that club."
Theron put two fingers to his forehead in a gesture Riven was coming to think of as his version of counting to ten.
"The Order doesn't extend research access to civilians," he said.
"The Order," Sable said, "also apparently let a seam-site under a civilian nightclub build to dangerous pressure levels without warning anyone. So perhaps the Order and I can discuss what we extend to whom once it has its own house in order." She picked up her coffee. "In the meantime, I want the full sensor dataset from the eastern sector's degraded zone. I can have a preliminary movement map in forty-eight hours."
Another pause.
"I'll speak to Commander Aldwyn," he said.
"Thank you," said Sable, entirely without gratitude in her voice.
When Theron left the room to make the call, Sable looked at Riven and dropped the professional composure entirely.
"Are you actually okay?" she said.
"I'm—" Riven turned the mark toward the light. "I don't know yet. Ask me after."
"After what?"
"After whatever comes next." She held Sable's gaze. "He was one of them, Sable. My father. He was a Warden. The accident—"
"Riven." Sable crossed the room and took her hand. Carefully, around the mark. "I know."
"You can't know, I just—"
"I know what it looks like when you're holding something enormous by yourself because you've decided it's not time to put it down yet." Sable squeezed once. "You don't have to. I'm here."
Riven looked at her.
"I need you to help me find what he left," she said. "There's something hidden in the eastern sector. He went there three times in his last six months and nobody in the Order knew. Whatever it is — it's the center of this entire thing. It's what the Voidwarden wants. And it's what's going to tell me why my father died." A pause. "I can't go in blind. I need the movement map."
"Then you'll have it," Sable said. "Forty-eight hours."
Riven nodded.
Through the wall, she could hear the low murmur of Theron on the call with Aldwyn, negotiating access he wasn't supposed to want for a civilian who wasn't supposed to be here.
She looked at her palm.
The mark pulsed once. Warm. Certain.
Pointing east.