Not surprisingly, Grimm can’t believe his eyes when Theresa and I turn up together at his flat. It’s amazing that he doesn’t shut the door in our faces, but luckily his curiosity gets the better of him. I like him for that; I know all about giving in to curiosity.

When Theresa has confessed all and Grimm has bombarded her with questions, he asks us in, apparently persuaded by her story.

‘Thank you,’ I say, as he shows us into his minimalist sitting room. ‘It was nice of you to listen.’

At first Grimm says nothing. I find it hard to look at him; my repugnance is tenacious. I’ve got so used to seeing him as my enemy that I am having trouble readjusting. I can sense that he’s experiencing similar difficulties.

‘Where do we go from here?’ he asks eventually.

‘We have two possibilities,’ I say. ‘Option number one: the three of us go to the police together and tell them everything. I just have a feeling that if we do that, Balder will worm his way out of things while Theresa and Bela get into serious trouble. Because, if you think about it, what’s Balder actually done? With a bit of luck we might be able to wangle a fine for him. But it’s equally possible that he gets off scot-free.’

‘He tried to kill me,’ Grimm cries. ‘And she helped him. She told me to go to the Prater on the evening of the eleventh. Why are we trusting her when she lied to us both?’

I nod.

‘We don’t have much reason to, it’s true. But I think Theresa knows she made a mistake.’

Theresa stares at the floor.

‘The problem is we can’t pin anything on Balder,’ I say.

‘What’s option number two?’ Grimm asks.

I smile.

‘We get our own back,’ I say. ‘Scare the hell out of him. The way he did with us.’

Grimm’s eyes narrow.

‘That’s too mild a punishment,’ he says and I think he’s damn right. But I let Theresa do the talking.

‘You have to know,’ she says, ‘that Balder is incredibly vain. He spends hours googling himself and reading articles about himself, and if anyone dares criticise him or even just makes fun of him, he completely freaks out. I once saw him throw a computer at the wall because an art blogger said he was overrated. No ordinary person can have any idea how over-inflated that man’s ego is.’

‘So, what do we do?’ Grimm asks.

‘Let the air out of him,’ I say.

‘I’ve been working closely with him for months,’ Theresa says. ‘The great Wolfgang Balder. The powerful, the sophisticated, the admired Wolfgang Balder. Larger than life, invulnerable, always in control. The man who baulks at nothing. That’s how he wants to be seen. It matters to him more than anything. If there’s one thing he can’t bear, it’s the thought of losing face.’

For a moment Grimm says nothing. Then he nods.

‘All right then. We unmask him. But how?’