Both their mouths opened. I turned and left before they could ask.

We put them in the canteen, along with a flustered Dr. Hunt-still clutching handfuls of paperwork-and left O'Gorman to keep an eye on them. Hunt gave us permission to search the site, with an alacrity that moved him further down the suspect list (Mark demanded to see our warrant, but backed off fast when I told him I'd be happy to get one if he didn't mind waiting around for a few hours), and Sophie and her team headed for the finds shed and started taping brown paper over the windows. Johnston, out on the dig, moved among the archaeologists with his notebook out, checking trowels and pulling people aside for brief tête-à-têtes.

"The same key fits all the Portakabins," Cassie said, coming out of the canteen. "Hunt, Mark and Damien have one each-not Sean. No spares. They all say they've never lost, lent or missed their keys."

"So let's start with the sheds," I said, "and then we can work our way outwards if we need to. Sam, will you and Cassie take the tools shed? Sweeney and I will do the office."

The office was tiny and crammed-shelves sagging with books and house-plants, desk piled with papers and mugs and bits of pottery and an elephantine, obsolete computer. Sweeney and I worked fast and methodically, pulling out drawers, taking down books and checking behind them and stacking them back roughly in place. I didn't actually expect to find anything. There was nowhere here to stash a body, and I was fairly sure the trowel and the plastic bag had been either dumped in the river or buried somewhere on the dig, where we would need the metal detector and huge amounts of luck and time to find them. All my hopes were pinned on Sophie and her team and whatever arcane rites they were performing in the finds shed. My hands moved automatically along the shelves; I was listening, so hard it nearly paralyzed me, for some sound from outside, footsteps, Sophie's voice calling. When Sweeney dropped a drawer and cursed softly, I almost screamed at him to shut up.

It was gradually dawning on me just how high I had staked on this. I could have simply rung Sophie and got her to come down and check out the finds shed, no need to mention it to anyone if it didn't pan out. Instead, I had taken over the entire site and pulled in just about every person who had anything to do with the investigation, and if this turned out to be a wild-goose chase I didn't even want to think about what O'Kelly would say.

After what felt like an hour I heard, outside, "Rob!" I leaped up from the floor, scattering papers everywhere, but it was Cassie's voice: clear, boyish, excited. She bounded up the steps, caught the door handle and swung round it into the office. "Rob, we've got it. The trowel. In the tools shed, under all these tarps-" She was flushed and breathless, and she had obviously completely forgotten that we were barely on speaking terms. I forgot it myself, for a moment; her voice sent the old, bright dart of warmth straight to my heart.

"Stay here," I said to Sweeney, "keep searching," and followed her. She was already running back to the tools shed, feet flashing as she jumped the ruts and puddles.

The tools shed was a mess: wheelbarrows at various wild angles, picks and shovels and mattocks tangled against the walls, great teetering stacks of dented metal buckets and foam kneeling mats and neon-yellow visibility vests (someone had written INSERT FOOT HERE, with an arrow pointing downwards, on the back of the top one), everything crusted in ragged layers of dried mud. A few people kept their bikes there. Cassie and Sam had been working from left to right; the left-hand side had that unmistakable post-search look, discreetly tidy and invaded.

Sam was kneeling at the back of the shed between a broken wheelbarrow and a heap of green tarpaulins, holding up the corner of the tarps with one gloved hand. We picked our way through the tools and squeezed in beside him.

The trowel had been jammed down behind the pile of tarps, between them and the wall; jammed hard enough that the point, when it caught halfway down, had gouged a rip into the tough material. There was no lightbulb and the shed was dim even with the big doors open, but Sam shone his torch on the handle: sc, big uneven letters with Gothic serifs, charred deep into the varnished wood.

There was a long silence; only the dog and the car alarm, on and on in the distance, with identical mechanical determination.

"I'd say the tarps aren't used very often," Sam said quietly. "They were behind everything else, under broken tools and all. And didn't Cooper say she was probably wrapped in something, the day before she was found?"

I stood up and dusted bits of muck off my knees. "Right here," I said. "Her family was going crazy looking for her, and she was right here all the time." I had got up too fast, and for a moment the shed rocked around me and receded; there was a high white buzz in my ears.

"Who's got the camera?" Cassie said. "We'll need to photograph this before we bag it."

"Sophie's lot," I said. "We'll need them to go over this place, too."

"And look," Sam said. He shone the torch over at the right-hand side of the shed, picked out a big plastic bag half full of gloves, those green rubber gardening gloves with woven backs. "If I needed gloves, I'd just take a pair out of there and throw them back in afterwards."

"Detectives!" Sophie yelled, somewhere outside. Her voice sounded tinny, compressed by the lowering sky. I jumped.

Cassie started to spring up, glanced back at the trowel. "Someone should probably-"

"I'll stay," Sam said. "You two go on ahead."

Sophie was on the steps of the finds shed, a black-light in her hand. "Yeah," she said, "definitely your crime scene. He tried to clean up, but…Come see."

The two baby techs were crammed into a corner, the guy holding two big black spray bottles, Helen with a video camera; her eyes were large and stunned over her mask. The finds shed was too small for five and the sinister, clinical incongruity the techs had brought with them turned it into some makeshift guerrilla torture chamber: paper covering the windows, bare lightbulb swinging overhead, masked and gloved figures waiting for their moment to step forward. "Stay back by the desk," Sophie said, "away from the shelves." She slammed the door-everyone flinched-and pressed tape back into place over the cracks.

Luminol reacts with even the tiniest amount of blood, making it glow under ultraviolet light. You can paint over a splattered wall, scrub a carpet till it looks brand-new, keep yourself off the radar for years or decades; luminol will resurrect the crime in delicate, merciless detail. If only Kiernan and McCabe had had luminol, I thought, they could have commandeered a crop-spraying plane and misted the wood, and fought down a hysterical desire to laugh. Cassie and I pressed back against the desk, inches apart. Sophie motioned to the boy tech for the spray, flicked on her black-light and switched off the overhead bulb. In the sudden darkness I could hear all of us breathing, five sets of lungs fighting for the dusty air.

Hiss of a spray bottle, the video camera's tiny red eye moving in. Sophie squatted and held her black-light close to the floor, near the shelves. "There," she said.

I heard Cassie's small, sharp intake of breath. The floor blazed blue-white with frantic patterns like some grotesque abstract painting: spattered arcs where blood had burst outwards, blotchy circles where it had pooled and started to dry, great swipes and scrub-marks where someone panting and desperate had tried to clean it away. It glowed like something radioactive from cracks between the floorboards, etched the rough grain of the wood in high relief. Sophie moved the black-light upwards and sprayed again: tiny droplets fanning across the bottom of the metal shelves, a smudge like a wild grabbing handprint. The darkness stripped away the finds shed, the messy papers and bags of broken pottery, and left us suspended in black space with the murder: luminescent, howling, replaying itself again and again before our eyes.