Kurt ground his teeth audibly. ‘I know they’re keys, boy. What do they open?’

Artemis shrugged. ‘Stuff. My locker. My scooter lock. A couple of diaries. Stuff.’

The security guard examined the keys. They were everyday keys, and wouldn’t open a complicated lock. But the bank had a no-key rule. Only safety deposit box keys were allowed through the metal detector.

‘Sorry. The keys stay here.’ Kurt undipped the ring, placing the keys on a flat tray.

‘You can pick them up on your way out.’

‘Can I go now?’

‘Yes,’ said Kurt. ‘Please do, but pass the bag through to your father first.’

Artemis handed the bag round the metal-detector arch to Butler. He passed through himself, setting off the buzzer.

Kurt followed him impatiently. ‘Do you have anything else metallic on you? A belt buckle? Some coins?’

‘Money?’ scoffed Artemis. ‘I wish.’

‘What’s setting off the detector, then?’ said Kurt, puzzled.

‘I think I know,’ said Artemis. He hooked a finger inside his top lip, pulling it up.

Two metal bands ran across his teeth.

‘A brace. That would do it,’ said Kurt. ‘The detector is extremely sensitive.’

Artemis removed his finger. ‘Should I take this out too? Rip it from my teeth?’

Kurt took the suggestion at face value. ‘No. I think we’re safe enough. Just go on through. But behave yourself in there. It’s a vault, not a playground.’ Kurt paused, pointing to a camera above their heads. ‘Remember, I’ll be watching.’

‘Watch all you like,’ said Artemis brazenly.

‘Oh, I will, boy. You so much as spit on one of those doors, and I’ll eject you from the premises. Forcibly.’

‘Oh, for heaven’s sake, Kurt,’ said Bertholt. ‘Don’t be so theatrical. Those are not network television cameras, you know.’

Bertholt ushered them through to the vault door.

‘I apologize for Kurt. He failed the special-forces exam and ended up here.