‘You know,’ she whispered, ‘there is absolutely no medical justification for the notion that men are sexually over the hill once they leave forty behind. And you are living proof of the opposite.’

‘This isn’t something that hard-bitten detectives are supposed to say.’ She bit his shoulder, gently. ‘ - Ouch! - but I love you, Doctor!’

‘That’s as well, my man, because I couldn’t live any more without your taste in music.’

On Sarah’s CD player, Joe Cocker, set on repeat programme, sang ‘We are the One’, for the eighth, or it could have been the eleventh, time. The choice had been Bob’s from a disc he had bought for her. One of the things that Sarah had discovered about her policeman lover was his remarkable talent for creating a mood.

Later, just after 9.00 p.m., as they drove down to Gullane, Bob slipped a cassette of Mendelssohn’s Scottish Symphony into the tapedeck. ‘Just to remind you where you are,’ he said.

They drove mostly in silence; Sarah was almost asleep by the time they reached their destination, lulled by the richness of the music.

They were smiling and completely relaxed when they arrived at the cottage.

‘And where the hell have you been?’ said Alex, rising to her feet as the living room door opened. Then she looked at the pair, Bob’s arm round Sarah’s shoulder. ‘On second thoughts, don’t answer that. There are certain things a father should not discuss with his daughter.’

Andy Martin sat stiffly on, rather than in, a big recliner armchair, managing somehow to make it look uncomfortable.

‘Sorry we’re late, Andy,’ Bob volunteered, still smiling. ‘Traffic was murder tonight!

‘Let’s go. The chef will be getting anxious.’

Alex drove Bob’s car on the ten-mile journey from Gullane to Haddington. They had reserved a table in a riverside restaurant. The proprietor wore a relieved smile as they entered.

‘Sorry, Jim,’ said Bob. ‘This lot kept me back!’

The meal was superb. King scallop chowder was followed by three fillet steaks, with Alex opting for baked sea-trout. As Bob finished off the second bottle of Cousino Macul, Sarah was happy to note that the unwinding process was almost complete.

They talked of music and movies, or rugby and royalty, the light, amusing conversation of a close group on an evening out.

Just before midnight, Alex, who had restricted herself to mineral water, pulled the Granada to a halt outside the friendly, family-owned hotel in Gullane which Bob had adopted years before as his local pub. It was one of his special places, and one in which Sarah felt completely at ease.

They settled into a table in the broad bay window.

At the restaurant, Andy had insisted on paying for the meal. ‘This is my celebration,’ he had declared. In the bar, Bob countered, astonishing Mac, the laid-back barman, by ordering champagne.

‘Christ, Bob, is it your birthday or something?’

‘No, you bugger, at the prices you charge, it’s yours!’

An hour later, with the car secured in the hotel park, the foursome walked home under a clear crisp winter sky. In the cottage, as Alex made up the bed in the guest room, Bob poured three glasses of Cockburn’s Special Reserve port. As Andy accepted his nightcap, he looked hard at his host.

‘Are you going to tell me, or not?’

Skinner smiled expansively. ‘Tell you what?’

‘You think you might have cracked it, don’t you? You think you’ve nailed our man.’

The smile grew even wider.

‘Well, since you’ve been vetted, I will tell you.

‘Even as we sit here sipping this fine port, two of our colleagues are out in the cold watching a certain house on the outskirts of Edinburgh, the occupant of which has been under constant observation for the last few days.

‘And once the Sheriff gives me the necessary warrant, as he will tomorrow - sorry, this morning - you and I, you for old times’ sake, will pay a call on the gentleman. There we will interview him in connection with the four Royal Mile murders, the murder of Rachel Jameson... ’

‘But that was a suicide, wasn’t it?’

‘Don’t you bloody believe it... and the murder in Glasgow of a certain Shun Lee.’

‘Who the hell is Shun Lee?’

‘Before he was axed, stabbed and castrated, he was a Chinese waiter, and a client of Miss Rachel Jameson.’

The revelation hung in the air for almost a minute. But even through the Cousino Macul, the champagne and the port, Martin’s mind was working. His face lit up in comprehension. ‘Not a client with a grudge. A victim.’

He looked sidelong at Skinner, with a quizzical smile.

‘The guy we’re going to visit. He wouldn’t be Japanese, would he?’