Rebus had wondered the same thing. He had no answer to offer.

`And Nemo or Memo?’

It was Lauderdale's turn, another respite from the coffee. 'I've got men on it, sir, checking libraries and phone directories, digging up meanings.’

`You've talked to the teenagers?’

'Yes, sir. They seem genuine enough.’

'And the person who gave them the key?’

'He didn't give it to them, sir, they took it without his knowledge. He's in his seventies and straighter than a plumbline.’

`Some builders I know,' said the Farmer, `could bend even a plumb-line.’

Rebus smiled. He knew those builders too.

`We're talking to everyone,' Lauderdale went on, 'who's been working in Mary King's Close.’

It seemed he had got the Farmer's joke.

`All right, John,' said the Farmer. `You were in the army, what about the tattoo?’

Yes, the tattoo. Rebus had known the conclusion everyone would jump to. From the case notes, they'd spent most of Sunday jumping to it. The Farmer was examining a photograph. It had been taken during Sunday's postmortem examination. The SOCOs on Saturday night had taken photos too, but those hadn't come out nearly as clearly.

The photo showed a tattoo on the victim's right forearm. It was a rough, self-inflicted affair, the kind you sometimes saw on teenagers, usually on the backs of hands. A needle and some blue ink, that's all you needed; that and a measure of luck that the thing wouldn't become infected. Those were all the victim had needed to prick the letters SaS into his skin.

`It's not the Special Air Service,' said Rebus.

`No?’

Rebus shook his head. 'For all sorts of reasons. You'd use a capital A for a start. More likely, if you wanted an SAS tattoo you'd go far the crest, the knife and wings and "Who dares wins", something like that.’

`Unless you didn't know anything about the regiment,' offered Lauderdale.

`Then why sport a tattoo?’