"Jesus," James muttered, looking over her shoulder at the complexity. "This is like a completely different system from what we've been working with."
"Because it is," Garrett said. "The official maps show you the bones—the main arteries where steam flows, the primary access points that maintenance crews use regularly. But the tunnels are more than that. They're a living system, constantly changing. Pipes corrode and leak. Water accumulates in low spots. Heat builds up in poorly ventilated chambers. And the older sections—the ones that were abandoned when they built newer systems—those are like ghost passages. Still there, still connected to the network, but forgotten."
Isla spread several of the maps across the conference table, studying the intricate web of passages Garrett had documented. She could see the three murder scenes marked—Access Point 7, where Langford had died, the abandoned section where Graves had been drowned, and Access Point 14, where Yamamoto should have died before the killer was forced to adapt.
"These locations," Isla said, tapping each murder site in turn. "What do they have in common from a structural perspective?"
Garrett moved closer, his weathered finger tracing paths between the marked points. "They're all junction chambers—places where multiple passages converge. That's important because it gives the killer options. Multiple entry points, multiple escape routes. You can't corner someone in a junction chamber because there's always another way out if you know the system well enough."
"And the environmental conditions?" James asked. "The extreme heat in the Langford scene, the water in the Graves scene?"
"Those weren't accidents," Garrett said flatly. "Whoever set those up knew exactly what conditions they'd find in those specific chambers. The heat in Chamber D-8 comes from a cluster of high-pressure lines that run through that section—normally regulated by automated controls, but easy enough to override if you have access to the junction boxes. The water in the decommissioned section accumulates because of poor drainage and condensation from the active pipes running overhead. It's been like that for years, getting deeper every winter."
Isla felt a chill that had nothing to do with the December cold seeping through the building's windows. "So the killer is using the infrastructure itself as a weapon. They're not bringing tools or equipment—they're just manipulating what's already there."
"Exactly." Garrett pulled one of his maps closer, pointing to several other locations marked in red ink. "And if I were planning more murders using the same methodology, these would be my high-risk targets. Junction E-6 has a steam release valve that could flood the chamber with superheated vapor if activated. Section H-2 has a carbon monoxide buildup problem—we're supposed to monitor it closely, but if someone disabled the sensors and lured a victim there..." He trailed off, the implication clear.
"Show us everything," Isla said, her voice tight with urgency. "Every high-risk location where the system could be weaponized."
For the next hour, Garrett walked them through his maps with the patience of someone who genuinely wanted to help. He identified seventeen locations that met his criteria—chambers where environmental conditions could be manipulated to create lethal scenarios, junction points with multiple access routes that would allow a killer to escape undetected, sections isolated enough that screams would never reach the surface.
Isla's stomach tightened as the list grew. Seventeen potential murder scenes, scattered throughout the tunnel network like landmines waiting to be triggered. They couldn't possibly monitor all of them effectively, not with their limited resources and the killer's apparent willingness to adapt when circumstances changed.
"Mr. Garrett," she said when he'd finished his presentation, "this has been incredibly helpful. But I have to ask—who else knows these tunnels the way you do? Who else would have this level of detailed knowledge?"
Garrett considered the question carefully, his expression troubled. "Not many people. Most of the newer maintenance workers stick to the active sections, follow the official maps, do their jobs without exploring beyond what's required. The old-timers who knew the system as well as I do—most of them are retired or dead."
"But there must be someone," James pressed. "Someone you've worked with, someone you've trained?"
"I've shown my maps to a few people over the years," Garrett admitted. "Safety inspectors, engineers, the occasional consultant who needed to understand the full scope of the system. But I've never given anyone copies. These maps—" he gestured to the papers spread across the table "—these are the only complete set that exists."
Isla exchanged a glance with James, both of them thinking the same thing. If Garrett's maps were unique, if his knowledge was singular, then how had their killer acquired the same intimate understanding of the tunnel system?
"We'd like to keep these," Isla said, indicating the maps. "For our investigation."
"Of course." Garrett nodded. "Keep them as long as you need. I've got most of it memorized anyway."
As he stood to leave, Isla felt compelled to add: "Mr. Garrett, be careful. If the killer knows the tunnels as well as you say they do, they might see you as a threat—someone who could identify them or interfere with their plans."
Garrett's weathered face softened slightly. "I appreciate the concern, Agent Rivers. But I've been working those tunnels for twenty-three years. I know how to stay safe down there."
The words should have been reassuring. Instead, they sent a chill down Isla's spine.
By 4 PM, the field office conference room had transformed into a command center. Isla stood at the whiteboard where she'd mapped out the seventeen high-risk locations Garrett had identified, color-coding them by threat level and accessibility. Lieutenant Morrison and three of his detectives occupied one side of the conference table, while James worked his laptop on the other side, coordinating with patrol units throughout the city.
"We don't have the manpower to cover all seventeen locations," Morrison said, his weathered face drawn with frustration. "Not effectively. We're already stretched thin with the existing investigation."
"Then we prioritize," Isla said, circling five locations in red marker. "These are the most isolated chambers with the most dangerous environmental conditions. If the killer follows their established pattern, they'll choose one of these for maximum impact."
"Assuming they stick to their pattern," James added. "They've already had to adapt once, with Yamamoto. They might change tactics completely."
The conference room door opened, and Thomas Garrett entered carrying two large thermoses and a brown paper bag. "Thought you all might need coffee and sandwiches," he said,setting them on the table. "Looks like you're planning a long night."
Isla felt a flash of irritation that he'd returned uninvited, followed immediately by guilt. The man was trying to help, was offering resources and expertise they desperately needed. "Mr. Garrett, you don't need to—"
"I want to help," he said simply, moving to look at the whiteboard. "Those are the locations I identified. Good choices for priority surveillance." He studied the map for a moment, then pointed to three additional access points Isla hadn't marked. "But you're missing the remote entrances. Access Points 18, 21, and 23—they're not on the official city maps because they were supposed to be sealed decades ago. But the seals have failed, and anyone who knows they exist could use them."
James pulled up a city map on his laptop. "Where are these located?"
