Sometimes I think he would love someone to rob the place, just so he could see some action.’

The door was a circular slab of steel, at least five metres in diameter. In spite of its size, it swung easily at Bertholt’s touch.

‘Perfectly balanced,’ explained the bank official. ‘A child could open it, until five thirty, when it shuts for the night. Naturally the vault is time locked. Nobody can open the door until eight thirty a.m. Not even the bank president.’

Beyond the vault door were rows and rows of steel deposit boxes of all shapes and sizes. Each box had a single rectangular keyhole on its face, surrounded by a fibre-optic light. At the moment all the lights glowed red.

Bertholt took a key from his pocket; it was attached to his belt by a woven-steel cable.

‘Of course the keys’ shape is not the only important thing,’ he said, inserting the key in a master keyhole. ‘The locks are also operated by microchip.’

Butler took a similar key from his wallet. ‘Are we ready?’

‘Whenever you are, sir.’

Butler ran his fingers over several boxes until he reached number seven hundred.

He inserted his key in the keyhole. ‘Ready.’

‘Very well, sir. On my mark. Three, two, one. Turn.’

Both men turned their keys simultaneously. The master key safeguard prevented a thief opening a box with a single key. If the two keys were not turned within one second of each other, the box would not open.

The light round both keys switched from red to green. The door on Butler’s safety deposit box popped open.

‘Thank you, Bertholt,’ said Butler, reaching into the box.

‘Of course, sir,’ replied Bertholt, almost bowing. ‘I’ll be right outside. Even with the camera, there is a three-minute inspection rule. So I’ll see you in one hundred and eighty seconds.’

Once the bank official had gone, Artemis shot his bodyguard a quizzical look.