AI The suspect's coat whipped around the corner of Shaftesbury Avenue, a flash of dark wool against the neon bleed of theatre marquees.
Quinn's boots hammered the pavement. Rain slicked every surface, turned the world into a funhouse of warped reflections. She'd been trailing Herrera for six blocks now, ever since she spotted him slipping out the side door of that Soho bar, the one with the green sign, carrying a leather satchel he clutched to his chest like a newborn.
"Stop! Metropolitan Police!"
He didn't stop. They never did.
She cut through an alley behind a Thai restaurant, garbage bags splitting under her feet and releasing a hot stench of rotting lemongrass. Herrera was fast for someone who didn't look like a runner, olive skin flushed, that ridiculous Saint Christopher medallion bouncing against his sternum as he vaulted a recycling bin. He landed clean. She noted the scar along his left forearm when his sleeve rode up. Knife wound. Old one. The kind you earn, not the kind you get from kitchen accidents.
"Herrera! Don't make this harder."
He glanced back. Warm brown eyes, wide with something worse than fear. Recognition.
He knew who she was.
That changed things.
Quinn pushed harder, lungs burning against the cold, wet air. Her warrant card slapped against her ribs in its inner pocket. The worn leather watch on her left wrist was soaked, and she could feel it sliding with each pump of her arms. Eighteen years she'd chased people through this city. She knew the rhythm. Suspects ran in patterns, gravitational pulls toward familiar ground. Herrera was heading north. Camden direction.
He burst out onto Charing Cross Road and nearly collided with a night bus. The driver leaned on the horn. Herrera stumbled, recovered, and darted across three lanes of traffic that parted around him like a school of startled fish. Quinn followed, palm up toward an oncoming taxi. Brakes screamed. The cabbie's expletive fogged his windscreen.
She gained ten metres on the crossing. Close enough now to hear his breathing, ragged and desperate, close enough to see the satchel's brass buckle glinting under streetlights. Whatever he carried mattered more to him than freedom.
Four blocks later, the architecture shifted. The polished shopfronts of the West End gave way to Camden's grittier teeth, market stalls shuttered and padlocked, the canal's damp breath rising between buildings. Herrera cut left down a street she knew, then right down one she didn't, some narrow passage between a tattoo parlour and a kebab shop that shouldn't have existed on any map she'd memorised.
The passage ended at a stairwell.
It descended into what looked like an old Tube entrance, except there was no TfL roundel, no signage, no indication that London Underground had ever claimed this hole in the ground. The tiled walls were grimy Victorian, pale cream ceramic darkened by a century of soot. A single bare bulb hung from a wire at the top of the stairs, swinging in a draft that rose from below, carrying with it a smell Quinn couldn't place. Copper and old paper and something else, something organic and wrong, like flowers left too long in stagnant water.
Herrera's footsteps echoed from the depths . Getting fainter.
Quinn stopped at the top of the stairwell. Rain ran down the back of her neck and pooled in the hollow of her collarbone. She gripped the iron railing. The metal was warm, which made no sense in this weather.
Three years ago, DS Morris had followed a suspect into a basement in Whitechapel. Routine pursuit. Drug runner, they thought. Morris went in alone because Quinn was thirty seconds behind, held up by a locked gate. When she got through, the basement was empty. No suspect. No Morris. Just his radio on the concrete floor, still crackling with static, and a symbol drawn on the wall in something that wasn't paint.
They found Morris four days later, wandering the Embankment in his socks. He couldn't remember the basement. Couldn't remember the suspect. Couldn't remember his own middle name. Medical retirement within the month. He still rang her sometimes, at three in the morning, asking about a door he could see when he closed his eyes. A door that moved.
Quinn stared down the stairwell.
Her phone buzzed. She ignored it.
Herrera's footsteps had stopped. Either he'd reached wherever he was going, or he was waiting for her. Neither option appealed.
She pulled her torch from her coat pocket. The beam cut through the dark, catching graffiti on the tiled walls as she descended. Not graffiti. Symbols. Spirals and intersecting lines that reminded her of circuit boards, if circuit boards had been designed by someone having a breakdown. The stairs went deeper than any legitimate Tube station. Twenty steps. Thirty. Forty. The air thickened, grew warm, tasted of iron filings on her tongue.
At the bottom, a corridor stretched ahead. Old rail tracks ran along the floor, rusted into the concrete. This had been a station once, she could see the platform edge, the curved ceiling, the alcoves where advertisements would have hung. But someone had repurposed the space.
Stalls lined both walls.
Dozens of them. Canvas awnings strung between pillars. Oil lanterns instead of electric light, casting everything in amber and shadow. The vendors were a cross-section of London's margins: a woman in surgical gloves arranging glass vials filled with liquids that shifted colour when Quinn's torchlight touched them. An old man with fingers too long for his hands, sorting through a tray of what looked like animal teeth . A teenage girl sitting on a Persian rug, surrounded by stacked books, who met Quinn's gaze with pupils that reflected the light like a cat's.
The underground market. She'd heard rumours. Intelligence reports she'd dismissed as informant fantasy. A black market for things that shouldn't exist, operating out of abandoned infrastructure, moving locations on a schedule she'd never been able to pin down.
Here it was. Real as the rain soaking her coat.
She killed her torch. The lantern light was enough, and the beam had already drawn attention. A dozen faces turned her direction. Conversation didn't stop, but it shifted register, dropped an octave. The way a pub falls quiet when the wrong person walks in.
Quinn straightened her spine. Military precision, Morris used to call it. Stand like you belong and people fill in the reasons.
She scanned the stalls. No sign of Herrera. The corridor branched ahead, splitting into what might have been maintenance tunnels. He could have taken any of them. She moved forward, keeping her hands visible, aware of every eye tracking her passage.
"Help you, love?"
The voice belonged to a man behind a counter made from a repurposed church pew. He sold maps. Hand-drawn, on parchment that looked older than the station. His fingers were stained with ink up to the wrist.
"Looking for someone."
"Course you are. Everyone's looking for someone down here." He smiled. Three gold teeth. "Question is, are they looking for you?"
"Olive skin. Dark hair. Carrying a leather satchel."
"Could be anyone."
Quinn leaned on the counter. Close enough to see the tattoo behind his ear. Same spiral pattern as the walls.
"Could be. But isn't."
The map seller's smile faded. He glanced past her shoulder. Quinn caught it, the micro-expression, the way his eyes flicked to something behind her and then returned with calculated blankness.
She didn't turn around. Turning around was how you showed weakness in a place like this. Instead she shifted her weight to the balls of her feet and watched the map seller's pupils for the reflection of whoever was approaching .
"You've got the wrong stall." His voice had dropped. "And the wrong market. And mate, you don't have a bone token, so technically you're not here."
"Bone token."
"Entry requirement. No token, no market. Rules aren't mine."
"Whose rules?"
He laughed. Short, humourless. The sound bounced off Victorian tiles and came back warped.
"Go home, officer."
Quinn's jaw tightened. She hadn't shown her warrant card. She hadn't identified herself since Shaftesbury Avenue, six blocks and a reality away. Which meant he'd been told . Which meant Herrera had come through here and sent word ahead.
Which meant Herrera was still close.
The reflection in the map seller's eyes shifted. The figure behind her had stopped moving. Five metres back, maybe six. Quinn catalogued escape routes. The branching tunnel to her left, partially blocked by a stall selling bottled smoke. The platform edge to her right, a drop onto dead tracks. Back the way she came, forty stairs up to the rain and the real world.
The figure behind her spoke. Spanish accent, soft, stripped of the panic she'd heard on the street.
"You shouldn't have followed me down here, Detective Quinn."
She turned.
Herrera stood between two stalls, the satchel open in his arms. Inside it, packed in straw like eggs, sat six glass vials filled with something that pulsed with its own faint light, a blue-white luminescence that cast his features in morgue-slab pallor. His hands were steady. His eyes were not.
"Those vials. What's in them?"
"Something that's going to save a lot of lives." He shifted the satchel behind him. "Or end yours, if you try to take them."
"That a threat?"
"A medical opinion."
The market had gone silent. Not quiet. Silent. The kind of silence that precedes violence, a held breath before a scream. Quinn registered it in her peripheral vision: stalls closing, canvas dropping, lanterns being hooded . The vendors were packing up. Fast and practised, like they'd rehearsed this exact scenario.
"Whatever you think you're doing here," Herrera said, "whatever case you think you're building, you need to walk away."
"I don't walk away."
"I know. That's what worries me." He took a step back, deeper into the tunnel's shadow. "You've been pulling threads for months. Surveillance on the Nest. ANPR on cars outside. Warrant applications that keep getting denied."
She said nothing.
"The denials aren't bureaucracy." Another step back. "They're protection. For you."
"From what?"
Herrera opened his mouth to answer.
Behind Quinn, at the far end of the platform, something scraped along the tracks. Metal on metal, a shriek that vibrated in her teeth. The remaining lanterns guttered. One blew out. In the sudden half-dark, the vials in Herrera's satchel burned brighter, and in their glow Quinn saw his face change, saw the colour drain from it like water from a broken glass.
"Too late," he whispered.
The scraping sound came again, closer, and every remaining light in the market went out at once.