‘They’ve come down from Hendon,’ he said. ‘This spotty shower are coming to the end of their course and sending them to me is an attempt to prepare them for the real world. A new initiative.’

‘I’ll wait, if that’s OK.’

He nodded. ‘Best to wait. Join them if you like.’

I followed them through into the Victorian sitting room, nine young men and three young women who were happy to be on a field trip, snickering at the fake fireplace and fake sash window.

They passed under the hangman’s noose and reached the table covered with weapons. Shotguns and rifles, replicas and the real thing, walking sticks that were really swords, umbrellas that were really handguns, and a glass case full of automatic weapons. By the time they went through the doorless opening into the museum proper, their laughter had stopped.

They saw the walking stick that turned into a sword that then turned into a knife – the Cop Killer. There was every kind of gun, every kind of knife – some of them dark with prehistoric blood. They paused longest before the display about the officers of the Metropolitan Police who had been killed in the line of duty.

By the end of their visit – and it doesn’t take very long to see the Black Museum – they were silent and shaken.

‘This place is a learning centre,’ Sergeant Caine told them, leaning against his cluttered desk and holding a mug that said BEST DAD IN THE WORLD. ‘I hope the lesson that you have learned today is that there are many ways to kill a policeman.’

They said nothing.

‘Thank you for visiting the Crime Museum at New Scotland Yard,’ Caine concluded with a formality I had not heard before. ‘Before you graduate from Hendon, I suggest you go to your school’s Simpson Hall where you will find the Metropolitan Police Book of Remembrance. Her Majesty the Queen has signed it and, before your studies come to an end, so should you.’ He looked at their serious young faces and nodded once. ‘Take care of yourself and take care of each other. Thank you, good luck and goodbye.’

When we were alone I opened my kitbag. Inside was a large evidence bag containing the Kevlar Stealth that had been worn by DCI Mallory on the night he died. It was almost new apart from the large stain on the right shoulder from the neck wound that had killed him.

Handling it with great care, I entrusted it to the safe keeping of Sergeant John Caine of the Black Museum, New Scotland Yard.

Chapter 31

31

STAN’S FAVOURITE CAFÉ in Regent’s Park was The Honest Sausage, just off The Broadwalk near London Zoo. We were at an outside table sharing a bacon sandwich, my dog on my lap, when she walked in. Sooner or later, every dog person in central London walks into The Honest Sausage.

‘You again,’ Natasha said.