Skinner and Martin walked the short distance, entering the Supreme Court buildings through the unmarked, anonymous, swing doors. They had almost passed the brightly-uniformed security men — known colloquially as the High Street Blues — when Martin stopped. ‘Hold on a minute, boss.’

He stepped over to the reception desk where a registration book lay open. Names, locations in the building, times of arrival and times of departure ran in four parallel columns. He scanned backwards through the list of signatures.

‘Here we are. Mortimer signed in at 9.11 p.m. and out at 4.02 a.m. Signed off for good about a minute later, I should think. I wonder what kept him working all night.’

‘It’s not all that unusual, Andy. The Library’s open twenty-four hours a day for advocates’ use, and these are busy people as a rule. The younger ones often live in small flats, and like to use this as an office as well as just a reading room.’

They walked across the Great Hall, beneath the magnificent hammer-beam roof, and past the stained glass window which reminds visitors that the Hall was, in centuries gone by, the home of Scotland’s Parliament.

The clock stood at only 8.22 a.m., but Roy Thornton, the Faculty of Advocates’ Officer and front-of-house manager, stood in his box at the Library entrance, resplendent in the formal uniform which was his working dress. It suited him. He had been, in an earlier career, Regimental Sergeant Major of the King’s Own Scottish Borderers.

He was a dark, trim man, with a neatly clipped moustache, and a face which gave a hint of his fondness for malt whisky. He and Skinner knew each other well, and the big detective respected the ex-soldier as the fountainhead of all knowledge about the head office of Scotland’s law business.

Thornton smiled in greeting. ‘Hello, Bob. Bit early for you, is it no’. Or have you not slept since that football team of yours was stuffed on Saturday!’ Thornton laughed. Football rivalry was another link between them. Roy Thornton was a Heart of Midlothian fanatic, while Skinner retained a boyhood loyalty to Motherwell. Both were Premier Division sides, and on the previous Saturday, Hearts had beaten Motherwell in a close and controversial match in Edinburgh.

Skinner grunted. ‘Had the ref locked up. He’s up in the Sheriff Court at ten o’clock. Charges are daylight robbery, high treason, buggery and anything else that I can think of between now and then.’

Thornton rocked back on his heels as he laughed. ‘So what brings you here, big fella. Looking to nobble an Advocate Depute?’

Skinner dropped the bantering tone. ‘No, Roy, what brings me here is bloody murder, most foul. Know a boy called Mortimer, one of yours?’

The term ‘boy’ is used widely in Scotland to denote any male person who is above the age of consent, but younger than the speaker.

Thornton nodded, his smile vanishing. ‘Young Mike? Aye, he’s a good lad. Why, what’s up?’

‘About four and a half hours ago, someone separated young Mike from his head — and I mean that — across the road in Advocates’ Close.’

The colour drained in an instant from Thornton’s face. ‘Sweet suffering Christ!’

Skinner gave him a few moments to absorb the news. ‘Listen, Roy, say no to this if you have any sense, but if you could make a formal identification now it could save the next of kin a load of grief.’

‘Sure, I’ll do that.’