Logan picked his way through the drizzle, down the long stairs from Union Street to the Green. At the bottom of the first flight a man was huddled in the boarded-up doorway of the sports shop hunched over a sticker-covered guitar, knocking out a reasonable rendition of some country and western tune. The damp woolly hat open in front of him held a couple of coppers and a few fifty-pence pieces. Logan dropped in a couple of pounds and kept on going. Down. And down. And down.

The Green was a lopsided rectangle, buried away in the foundations of the city, lined with tall granite buildings, their grey faces darkened by moisture, lights making glowing orbs in the misty drizzle. Some sort of birthday party was underway in the open-air eating area outside Café 52, everyone huddled under a big green patio umbrella as they belted out ‘Happy Birthday To You’, a cake topped with dozens of candles blazing away.

Logan kept going, across the slippery cobblestones, towards the back end of Aberdeen Market – a semicircular lump of seventies concrete, its windows dark, everyone shut up for the night. Down one side, Correction Wynd cut straight under Union Street, a handful of restaurants glowing in the shadow of St Nicholas Kirk. But right ahead, the road disappeared into the gloom.

Seagulls screamed abuse from the slate rooftops far above as he followed East Green into the bowels of the city and out of the rain.

A row of neon squiggles glowed around the entrance to Blofeld’s Secret Underground Lair, casting multicoloured light on a big bald bloke in a white shirt and bow tie, standing all on his own. Looking for someone to bounce as dance music thunked out of the door behind him.

At the end of the road, where it hooked around before climbing back up onto Nether Kirkgate, a mobile catering unit was parked up on the narrow kerb. The thing was a rec-tangular white trailer with a fold-down flap on the front beneath a sign ‘LOLA & RUDY’S TASTY TREATS’. Steam curled from the open hatch, and a handful of figures formed an orderly queue in front of it. About a dozen others were gathered in small groups, eating and talking over the growl of a diesel generator. At least three of them were nightshift CID, blending in like lumps of coal in a bowl of porridge.

They weren’t the only ones: a brick outhouse with a crew cut, dressed in black jeans and a red T-shirt, stood guard a hundred yards from the catering unit: Mr Muscle from the hotel. The one who spoke like he was giving evidence. Another heavy stood at the far end, hands folded in front of his groin, narrow eyes constantly moving back and forth.

No way Agnes Garfield would come anywhere near the place with that kind of security hanging around.

Logan took two steps towards them, then stopped.