AI "Tell me how he walked through a locked wall."
Harlow stepped past the SOCO kneeling with his kit, the yellow tape brushing her shoulder, her boot soles gritting on scattered glass. The body lay crumpled half on, half off the bottom flight of concrete steps that led to a bricked archway, eyes open, mouth set in a slack, crooked shape that never counted as peaceful.
"Morning to you too." The detective sergeant beside her shifted his weight , hands buried in his pockets. "He did not walk through the wall. He fell down the stairs. We live in a simple world, Quinn. Let it comfort you."
She ignored him. The wall had her attention. Old brick, soot-stained, mortar crumbling in places. Someone had painted over the arch in thick white years before, then graffiti artists had claimed it, layer over layer of tags and cartoon teeth. No cracks, no loose bricks. No door.
She crouched beside the dead man.
Tall, late thirties, hair clipped short in an expensive cut that still held its shape, suit creased now but good wool, shoes polished enough to pick up the stark strip lights above. His head lay at a sharp angle against the step. Neck broken, or close to it. Blood had seeped from his right ear and pooled beneath, a sticky halo on the concrete.
Harlow studied the pool. Tight circumference. No splatter up the risers. No cast off.
"Slip and tumble." The sergeant leaned on the rail, metal groaning under his weight . "No sign of struggle, no drag marks. CCTV caught him heading down alone. Station staff locked up the minute he finished his shift, came back at six, found him like this. Clean enough for a Monday."
"His name."
"Michael Rutherford. Operations supervisor for the line. Lived alone in Kentish Town. Union rep, according to the badge on his lanyard." The sergeant watched her fingers . "You going to prod him or can I call the coroner before lunch?"
Harlow pressed two fingers into the cloth of the shirt, just under the sternum. Still faint warmth . He had not lain long before someone found him. A few hours at most.
She moved to his hands. No defensive wounds, no torn nails, a faint smear of black grease on his left thumb. Grease that did not match the clean concrete around them.
"Pathologist can confirm," the sergeant said . "He took a bad step. Head met concrete. End of story."
"Concrete on his scalp, yes," she murmured. "Concrete dust on his back, shoulders, both arms." She traced the ghost of dust with her gloved thumb. "He rolled, at least twice. You roll if you lose balance and momentum carries you down. Yet his tie still sits under the knot of his collar."
"Some people fall neat."
She glanced up.
"Run me through it, Malik."
He sighed, but straightened a little, professional instinct winning over sarcasm.
"Right. Closed spur off Camden Town. They stopped trains using this platform years ago when they modernised. They use it for staff access and storage now. Rutherford had authority to be here. Station CCTV shows him leaving the control room at about half one, heading for a restricted door with a keycard. Camera outside the door catches him going through. No one else enters or exits between then and when staff find him around five."
"No cameras down here."
"Budget cuts. Plus ghosts." Malik grinned without humour. "Platform supervisor says no one likes this bit. Old London, old stories, all that."
Harlow stood.
Old London. The words sat under her tongue like iron.
She looked up the stairs. Twelve steps, shallow rise, steel rail on either side. At the top, a grey door with flaking paint stood propped open by a yellow evidence cone. Light bled from the station corridor beyond, the hum of announcements muffled by the angle. A crime scene photographer hovered there, waiting.
Harlow climbed halfway, then stopped and turned, surveying.
Steps clean, apart from SOCO's powder and a few scuffs. No broad smear of blood like a body had bounced end over end. No pattern of heels striking, no chips out of the concrete.
She walked back down, slow, heel to toe, copied his route. Her boots found each edge with mechanical precision. She leaned as if her shoulder had clipped the rail. Solid, cold, no give. To fall, he would have had to misjudge the first step, pitch forward and fail to catch anything.
"Station staff say he knew this place like second nature," she said.
"They also say the air down here whispers in Polish." Malik snorted. "Union rep, long hours, stress, maybe a hip flask in his locker. He trips, no one sees because no one comes here. Occam's razor."
"In my experience, Occam never dealt with Network Rail."
She crouched again at Rutherford's head. The right side of his skull had taken the impact. Fracture line visible where hair met skin, a pale gleam under the gore. His right shoulder looked lower than his left, suit pulling tight across the back in an odd way, like something had yanked down hard.
She peeled the jacket open.
"Careful with the pockets," Malik said.
"Always."
Inner lining. Wallet. Oyster card. A small brass weight that dropped into her palm with an unexpected heaviness.
Not a weight . A compass.
She turned it over. Palm-sized, casing dulled to a greenish bloom, etched along the edge with tiny sigils that caught the light like scratches. The glass face felt warm against her glove. The needle inside did not rest on north. It jittered, then snapped to point not down the corridor, not towards the tracks, but sideways .
Directly at the walled arch at the bottom of the stairs.
"Souvenir from a market stall," Malik said. "Rutherford liked bric-a-brac. His flat's full of it, apparently."
"You have been."
"Uniform cleared it. I read the notes." He peered at the compass . "Cheap tat. See, the needle sticks."
The needle held steady now, though Harlow twisted her wrist, angling the case. It fought to keep aim at the same fixed spot.
She closed her fingers around it. For an instant, the skin along her arm prickled as if she had reached into a freezer.
"This was in his inner pocket," she said. "Left side, close to the heart. You tuck cheap tat into that pocket?"
"He was on shift. He tucked whatever he wanted where he wanted. He also had a novelty keyring shaped like a duck in his trouser pocket, if you feel that helps build character."
Harlow rose and crossed to the wall.
Up close, the graffiti turned untidy. Swirls and tags stuttered over older paint. Someone had traced a line of symbols along the base, near the floor, in black marker. Shapes of letters, almost, then slanted away into angles that refused the Roman alphabet.
Harlow saw them and the breath in her lungs went sharp.
Three years vanished. Rain on warehouse glass resurfaced, the stink of damp rope, her partner's hand on her forearm as they both stepped into a chalk circle. Morris had joked about hipster witches. He had laughed. The symbols on that floor had glowed once, a thin dull red under the harsh inspection lamps.
The marks on this wall echoed them. Cruder, uneven, but close.
"Someone has doodled," Malik said, gaze following hers . "Kids with time on their hands."
She traced the first symbol through the latex glove, not quite touching, expecting heat . She felt brick, cold and rough. The marker bled at the edges in thin spiderwebs.
The compass warmed in her other hand.
"Path team swept this?" she asked.
"Top to bottom. No footprints they did not expect. Our victim, plus staff who found him, plus first responders. Nothing else."
"No prints on the rail consistent with clutching. No scuff at the edge consistent with a slip."
"He could have caught himself and still gone over."
She exhaled, slow.
"Rutherford walked down these stairs," she said. "Head level. Confident. He reaches this landing. Then his neck breaks, his body lands across the last three steps, he bleeds precisely there, and your answer is 'he slipped'."
"You are doing your thing."
"What thing."
"The thing where you smell ghosts." Malik's mouth twitched. "Look, Quinn, I know Morris died bad. But this scene does not want a haunting, it wants an incident report."
She stared at him. He dropped his eyes first.
"This scene wants the truth," she said.
He rubbed his jaw.
"Fine. Impress me. What do you see that the rest of us fools have missed?"
She turned away from him, back to the body.
The tie. Still knotted. Slightly askew but not yanked loose. Shirt buttons intact, no tear where a hand grabbed. Yet the bruise on Rutherford's right upper arm that bloomed under the white cotton, a deep patch of discoloured skin, looked like a grip mark .
She tugged the sleeve up, exposing the bruise in full. Four oval impressions along the bicep, one on the underside.
"He met someone," she said. "They stood close enough to grasp him. They held tight enough to bruise. But your cameras show no one."
"No one went through that door after him. Unless they used a cloak of invisibility."
"Or unless the cameras did not see the entrance they used."
She looked again at the arch.
The compass needle quivered , steadying, insistently aimed.
"If you tell me there is a secret door," Malik said, "I will put in for a transfer to Traffic before the end of the shift."
"You read cartoons as a child. With the hero who pulls a book and the shelf moves."
"I read law textbooks. You surprise me every day."
She stepped close, so the stained brick filled her vision. The mortar line at chest height looked thicker in places, a careless smear as if someone had rushed the job. The lower row of bricks carried more dust than the ones above, despite less reach from idle hands. The concrete floor in front of the arch showed a faint semi-circle of wear, a difference in tone that spoke of something opening and closing across it. Not often, but enough .
She knelt and touched the floor. Grime met her glove in a thin film. A tiny shard of white, caught in the line where floor met wall, gleamed.
She picked it out. Bone, no bigger than a fingernail clipping, carved along one edge. The surface held a faint pattern of lines.
Malik peered.
"Chicken takeaway."
"Your appetite disturbs me."
She tucked the fragment into an evidence bag one of the SOCOs handed over without comment.
"Did uniform search for access points to old tunnels?"
"They walked the lot. No breaches." Malik hesitated. "Though one of the PCs flagged a door on the service map that they could not find in person. Probably a drafting error."
"Show me."
He dug his phone out, opened a photo from his email. A PDF of station schematics, yellowed in the scan. He held it where she could see. A rectangle marked 'Staff Access 12B' sat directly where she stood.
"And in reality?" she said.
"In reality, we have concrete and a corpse."
She straightened.
"Pathologist will tell us cause and time of death," she said. "Computer unit can pull full logs from card access doors. I want Rutherford's phone records, bank statements, any complaints made about him in the last six months, any he made."
Malik raised both eyebrows.
"You think someone killed a Tube supervisor over a timetable."
"No one falls this clean."
"People fall down stairs all the time."
"Then they should make more mess of it."
He opened his mouth, closed it, looked past her towards the tracks. A low rumble drifted through the tunnel, a ghost of a train long gone. This line did not see service, yet the air vibrated as if something heavy ran under their feet.
"You hear that?" he said.
"Old city settling."
"So we agree this place is cursed."
The rumble faded. Harlow rolled the compass between her fingers.
"There is a market," she said, more to herself than to him . "Unlicensed, off-book. Moves around. People whisper . They say you reach it through places that do not exist on maps."
Malik stared.
"Please tell me you are not crowd-sourcing crime scene theory from urban legends."
"Uniform did not find Access 12B because they looked for a door. Perhaps they needed a key."
She lifted the bone fragment in its plastic.
"A chicken bone key," Malik said. "Of course."
"And a compass that points nowhere on any normal axis."
"It points at a wall."
"It points at an entrance."
She stepped so close the brick almost brushed her nose. Up close, the marker sigils blurred, but one stood clear. A spiral, split with a straight line, flanked by two dots. She had seen that one drawn on warehouse concrete, in chalk that smelled like old coins .
Her fingers, even through the glove, felt the faintest indentation.
She touched the symbol with the hand that still held the compass.
Heat flared against her palm, sharp and sudden. Her vision tightened at the edges.
Behind her, someone swore.
The mortar line under her hand pulsed . Not a trick of light, not fatigue. The brick face throbbed once, like a slow heartbeat.
"Harlow," Malik said. "Step away from the wall."
The compass needle spun in a tight frantic circle, then snapped forward so hard the glass face chimed.
A hairline crack lanced across the brick, vertical, starting at the symbol. Dust hissed from the split and pattered onto her boots. The air that leaked through smelled of incense and cold iron, and something else beneath, sharp and coppery.
Harlow yanked her hand back.
The crack widened in front of her like a mouth beginning to open.