This particular Grebe Tours party was American. They’d flown in almost a month ago for what Bell called the ‘Full British Tour’ – Canterbury, Salisbury, Stonehenge, London, Stratford, York, the Lake District, Trossachs, Highlands, and Edinburgh.

‘This is just about the last stop,’ he said. ‘For which relief much thanks, I can tell you. They’re nice people mind, I’m not saying they’re not, but… demanding. Yes, that’s what it is. If a Brit doesn’t quite understand what’s been said to him, or if something isn’t quite right, or whatever, they tend to keep their gobs shut. But Americans…’ He rolled his eyeballs. ‘Americans,’ he repeated, as though it explained all.

It did. Less than an hour later, Rebus was addressing a packed, seated crowd of forty American tourists in a room off the large dining-room. He had barely given them his rank when a hand shot into the air.

‘Er… yes?’

The elderly woman stood up. ‘Sir, are you from Scotland Yard?’

Rebus shook his head. ‘Scotland Yard’s in London.’

She was still standing. ‘Now why is that?’ she asked. Rebus had no answer to this, but someone else suggested that it was because that part of London was called Scotland Yard. Yes, but why was it called Scotland Yard in the first place? The woman had sat down now, but all around her was discussion and conjecture. Rebus looked towards Tony Bell, who rose from his own seat and succeeded in quietening things down.

Eventually, Rebus was able to make his point. ‘We’re interested’, he said, ‘in a visitor to Edinburgh Castle this morning. You may have seen someone while you were there, someone standing by the walls, looking towards the Scott Monument. He or she might have been standing there for some time. If that means something to anybody, I’d like you to tell me about it. At the same time, it’s possible that those of you who took photographs of your visit may have by chance snapped the person we’re looking for. If any of you have cameras, I’d like to see the photos you took this morning.’

He was in luck. Nobody remembered seeing anyone suspicious – they were too busy looking at the sights. But two photographers had used polaroids, and another had taken his film into a same-day processor at lunchtime and so had the glossy photographs with him. Rebus studied these while Tony Bell went over the next day’s arrangements with the group. The polaroid photos were badly taken, often blurry, with people in the background reduced to matchstick men. But the same-day photos were excellent, sharply focused 35 mm jobs. As the tour party left the room, en route for dinner, Tony Bell came over to where Rebus was sitting and asked the question he knew he himself would be asked more than once over dinner.

‘Any joy?’

‘Maybe,’ Rebus admitted. ‘These two people keep cropping up.’ He spread five photographs out in front of him. In two, a middle-aged woman was caught in the background, staring out over the wall she was leaning on. Leaning on, or hiding behind? In another two, a man in his late twenties or early thirties stood in similar pose, but with a more upright stance. In one photo, they could both be seen half turning with smiles on their faces towards the camera.

‘No.’ Tony Bell was shaking his head. ‘They might look like wanted criminals, but they’re in our party. I think Mrs Eglinton was sitting in the back row near the door, beside her husband. You probably didn’t see her. But Shaw Berkely was in the second row, over to one side. I’m surprised you didn’t see him. Actually, I take that back. He has this gift of being innocuous. Never asks questions or complains. Mind you, I think he’s seen most of this before.’

‘Oh?’ Rebus was gathering the photos together.

‘He told me he’d been to Britain before on holiday.’

‘And there’s nothing between him and-?’ Rebus was pointing to the photograph of the man and woman together.

‘Him and Mrs Eglinton?’ Bell seemed genuinely amused. ‘I don’t know – maybe. She certainly mothers him a bit.’

Rebus was still studying the print. ‘Is he the youngest person on the tour?’

‘By about ten years. Sad story really. His mother died, and after the funeral he said he just had to get away. Went into the travel agent’s and we were offering a reduction for late bookings.’

‘His father’s dead too, then?’

‘That’s right. I got his life story one night late in the bar. On a tour, I get everyone’s story sooner or later.’

Rebus flipped through the sheaf of photos a final time. Nothing new presented itself to him. ‘And you were at the castle between about half past eleven and quarter to one?’

‘Just as I told you.’

‘Oh well.’ Rebus sighed. ‘I don’t think-’

‘Inspector?’ It was the receptionist, her head peering around the door. ‘There’s a call for you.’

It was Superintendent Watson. He was concise, factual. ‘Withdrew five hundred pounds from each of four accounts, all on the same day, and in plenty of time for the rendezvous at the Café Royal.’

‘So presumably he paid up.’

‘But did he get the letters back?’

‘Mmm. Has Lady Scott had a look for them?’

‘Yes, we’ve been through the study – not thoroughly, there’s too much stuff in there for that. But we’ve had a look.’ That ‘we’ sounded comfortable, sounded as though Watson had already got his feet under the table. ‘So what now, John?’

‘I’m coming over, if you’ve no objection, sir. With respect, I’d like a look at Sir Walter’s office for myself…’

He went in search of Tony Bell, just so he could say thanks and goodbye. But he wasn’t in the musty conference room, and he wasn’t in the dining-room. He was in the bar, standing with one foot on the bar rail as he shared a joke with the woman he had called Mrs Eglinton. Rebus did not interrupt, but he did wink at the phone-bound receptionist as he passed her, then pushed his way out of the Castellain Hotel’s double doors just as the wheezing of a bus’s air brakes signalled the arrival of yet more human cargo.

There was no overhead lighting in Sir Walter Scott’s study, but there were numerous floor lamps, desk lamps, and angle-poises. Rebus switched on as many as worked. Most were antiquated, with wiring to match, but there was one newish anglepoise attached to the bookcase, pointing inwards towards the collection of Scott’s writings. There was a comfortable chair beside this lamp, and an ashtray on the floor between chair and bookcase.

When Watson put his head around the door, Rebus was seated in this chair, elbows resting on his knees, and chin resting between the cupped palms of both hands.

‘Margaret – that is, Lady Scott – she wondered if you wanted anything.’

‘I want those letters.’

‘I think she meant something feasible – like tea or coffee.’

Rebus shook his head. ‘Maybe later, sir.’

Watson nodded, made to retreat, then thought of something. ‘They got him down in the end. Had to use a winch. Not very dignified, but what can you do? I just hope the papers don’t print any pictures.’

‘Why don’t you have a word with the editors, just to be on the safe side?’

‘I might just do that, John.’ Watson nodded. ‘Yes, I might just do that.’

Alone again, Rebus rose from his chair and opened the glass doors of the bookcase. The position of chair, ashtray and lamp was interesting. It was as though Sir Walter had been reading volumes from these shelves, from his namesake’s collected works. Rebus ran a finger over the spines. A few he had heard of; the vast majority he had not. One was titled Castle Dangerous. He smiled grimly at that. Dangerous, all right; or in Sir Walter’s case, quite lethal. He angled the light farther into the bookcase. The dust on a row of books had been disturbed. Rebus pushed with one finger against the spine of a volume, and the book slid a good two inches back until it rested against the solid wall behind the bookcase. Two uniform inches of space for the whole of this row. Rebus reached a hand down behind the row of books and ran it along the shelf. He met resistance, and drew the hand out again, now clutching a sheaf of papers. Sir Walter had probably thought it as good a hiding place as any – a poor testament to Scott the novelist’s powers of attraction. Rebus sat down in the chair again, brought the anglepoise closer, and began to sift through what he’d found.