Pünd nodded. ‘You will permit me …?’

He walked into the corridor between the wardrobes and crouched down beside the safe, resting a hand on the steel surface. Given that it weighed more than two hundred pounds, the safe was smaller than he had imagined. It had the proportions of a deck of cards, taller than it was deep, completely bare but for a handle, a combination lock and, next to it, a keyhole. The name of the manufacturer was written across the top. The door fitted absolutely flush with the outer shell, making it impossible to slip even a sheet of paper inside, let alone the tip of a crowbar. The safe was grey in colour. Its setting was almost theatrical, with dark red wallpaper on three sides, again picking up the Chinese theme from the bedroom. Pünd did not try to move it. He could tell at once that it was utterly solid, bolted into place.

‘Would it be possible for you to open the safe?’ Pünd asked.

‘Of course. But it is empty now.’

‘The police examined it?’

‘Yes. They were meticulous. No fingerprints. No forced entry. Nothing.’

Pargeter leaned forward and began to spin the combination dial. Sixteen to the left, five to the right, back to twenty-two on the left … there were seven separate movements before the wheel flies aligned. He turned the key in the lock, then pulled the handle. There was a click and the door opened. Looking past him, Pünd saw that there was indeed nothing inside.

Pünd swung the safe door open and shut again, feeling the weight of it, its solidity, in his hand. There was nothing more to be seen. He straightened up and turned his attention to the surrounding walls, tapping them with his knuckles as if searching for a secret passage. Elaine Pargeter was watching him from the bedroom and did not look impressed. Pünd ran a finger over a small tear in the wallpaper, then rubbed his thumb against it, deep in thought. The safe was locked again. The three of them went back downstairs.

They went into the drawing room and Pünd accepted a second offer of coffee, which was brought in by the maid, who had been away on the night of the crime and seemed unaware that anything untoward had taken place. The Pargeters were sitting opposite him on a sofa. He was perched, slightly above them, on a high-backed antique chair that might have come out of a church.

‘It might be helpful to speak to your friend, Mr Berkeley,’ he said.

‘I’m not sure what he can tell you,’ Pargeter replied. ‘He gave the police a full statement and now he’s back in New York. But I can put a call into Shell for you, if you like.’

‘The police … ’ Pünd took a sip of his coffee, carefully lowering the cup onto its saucer, which he had balanced on his knee. He turned to Elaine. ‘It was you, Mrs Pargeter, who telephoned them?’

‘Yes. Detective Inspector Gilbert arrived about thirty minutes later. He had a sergeant with him, a pleasant young man. It was two o’clock in the morning by that time; the two of them were on night duty. They interviewed us in the room where we’re sitting now and asked a great many questions. They went upstairs and they also looked round the side of the house, where the window had been broken. They told us not to go into the closet – John had been right about that. The next morning we had a whole crowd of people from Scotland Yard: forensics, photographers, the lot!’

‘I would be interested to know if, at any stage, the police suggested that you yourself might be involved in the disappearance of the diamond.’

‘No. Quite the opposite,’ Pargeter said. ‘They were scrupulously polite. They were interested in the safe and the way it operated. They examined the key – they had obviously never seen anything quite like it.’ He paused. ‘They did, however, want to know who else had been given the combination.’

‘You told them the same as you have told me.’

‘Exactly. There are only three people in the world who have it. My wife, myself and my lawyer.’

‘But that is not true, Mr Pargeter.’

‘What?’ The businessman glanced angrily at Pünd, unhappy at being contradicted.

‘Nobody else knows the combination,’ his wife insisted.

Pünd closed his eyes. ‘Sixteen left, five right, twenty-two left, thirty right, twenty-five left, eleven right, thirty-nine left.’ He opened them again. ‘That is correct, is it not?’

Pargeter flushed. ‘You were watching me when I opened it!’

‘That is exactly what I did.’

‘Well, that’s a cute trick, Mr Pünd, but I’m not quite sure what point you are trying to make. Nobody else ever came into that room with me apart from my wife, and for what it’s worth, I saw you looking over my shoulder. You’ve got a good memory, but you might as well forget those numbers. They don’t matter any more. That horse has bolted, as the saying goes. I’ll be getting rid of the safe and buying a new one.’

‘Ah, yes! You do not close the door after the horse has bolted. That is the saying to which you refer.’ Pünd smiled. ‘And for me, you open it!’

‘I’m sorry?’

Pünd got to his feet. ‘I need to make a few enquiries,’ he said. ‘But it is clear to me how the Ludendorff Diamond and all the other contents were removed from the safe and by whom. You will be in England for a few more days?’

‘I’ll stay as long as it takes.’

‘Not long, Mr Pargeter. Then all will be revealed!’

The arrests had taken place four days later and in the end the diamond, all of Mrs Pargeter’s jewellery and most of the money had been recovered. And Pargeter had been true to his word. Sitting in his brand-new living room with his sherry and his cigarette, Pünd thought about the cheque that had arrived with a brief note of thanks, more money than he had earned in several years. He had put down a deposit on Tanner Court the same day. He had bought new furniture, including a handsome Biedermeier desk. He had hired a secretary to assist him with his administrative work. That reminded him. He must tell Miss Cain to get rid of the bed. That had definitely been a mistake.

And the culprits?

It hadn’t taken him long to discover that John Berkeley, Pargeter’s old school friend, had serious money problems. Pargeter had more or less told him that himself. He had stayed in the house because he couldn’t afford a hotel. A little further digging had revealed that it was no coincidence that Detective Inspector Gilbert (who was getting divorced) and Detective Sergeant Dickinson (who had a fondness for racing) had been in the Knightsbridge police station at half past one in the morning. They had actually volunteered for the night shift, knowing they would be called out. It had taken three of them to get past the security of the world’s most impregnable safe, and although Pünd couldn’t be certain of all the details, there was only one way it could have worked.

Berkeley had been the key. He had left with the Pargeters, knowing that the house was empty apart from an elderly butler who would sleep through the whole thing. While they were away, Dickinson had broken in, smashing a window and silencing the alarms. He would have had plenty of time to prepare the scene for the robbery. First, he had placed a simple flat – a piece of theatrical scenery covered in dark red Chinese wallpaper – in front of the locked safe. Then he had brought in a second safe, a perfect replica of the Sentry model, but made out of much lighter material – painted wood – with the door open and the interior obviously empty.

When the Pargeters had got back from the party, Berkeley had ‘spotted’ the broken pieces of glass on the drive. It was actually important that Pargeter and his wife should realise that they had been burgled before they went into the house; it would influence how they behaved. Of course, they went straight to the safe and once again it was Berkeley who had taken control of the situation. Those were the exact words that Pargeter had used. He had stopped them from turning on the light in the alcove. He had told them not to go in. From a distance of ten feet, and even with the reflected light, the illusion would have been perfect. The fake wall blended in with the real one. The real safe was concealed behind it. The wooden safe was open and empty.