‘And what would you do, Detective?’ she said, laughing at my eagerness to get out of that broken-hearted home. ‘If it was your daughter – in those rooms – with those men – what would you do about it?’

I said nothing.

I couldn’t look at her.

She followed us to the door.

‘You catch them?’ she said. ‘The men that hanged Mahmud Irani? Give them a medal.’

We were walking to the car when I looked up and saw the face of the girl at the window. Sofi. The curtain closed and she was gone. Edie and I didn’t speak until we were back in the car.

‘You didn’t answer her question,’ Edie said. ‘What would you do if it was Scout, Max?’

‘Oh, give me a break, Edie.’

We both knew what I would do.

6

There is a hanging tree in the Black Museum.

It is a horizontal wooden triangle supported by three legs and it rests in a quiet corner of what is officially known as the Crime Museum. It is draped with perhaps two dozen hangman’s nooses, all individually labelled with the name of the man or woman they executed.

‘It’s a replica of the triple-tree at Tyburn,’ said Sergeant John Caine, the keeper of the Black Museum. ‘The gallows was portable, and that’s one of the reasons that nobody can ever agree about where Tyburn actually stood, although they were hanging people there for centuries.’ He sipped from a mug that said BEST DAD IN THE WORLD. ‘They moved it about, see.’

I touched one of the nooses.

It was just four thin strands of rope running through a metal eyelet to form the noose. Other ropes were much thicker, twice the size, strands of heavy rope woven together and running through a big brass thimble to form the noose.

‘The thin ones date from the eighteenth century,’ Sergeant Caine said. ‘The thicker ones are more modern. They go all the way to 1969, when the death penalty was abolished in this country.’

‘You’ve got a lot of ropes in here, John. I never noticed before.’

‘We’ve hanged a lot of people in this country. You could fill a stadium with the people they hanged at Tyburn alone. Some of these nooses date back to 1810 when there were 222 offences that were punishable by hanging, including robbing a rabbit warren and shoplifting.’

‘But why would anyone use hanging to murder someone?’ I said, touching one of the nooses as if it would reveal the answer. ‘Why not just shoot them or stab them?’

‘Because they want revenge,’ said Sergeant John Caine. ‘Let me show you something.’

It was a battered black leather suitcase. Inside was a length of rope, a leg strap and a hood that had once been white but was now yellow with age, folded as neatly as a handkerchief.