‘Cosimo!’ exclaimed Vitale. ‘A stage effect? Explain this to me!’ He gestured at the hanging mass of tubing.

‘All in good time, Leo,’ said Fortuny.

‘Ah yes,’ said Holmes. ‘I can see it.’

‘Holmes, should we not all repair to some safer location?’ I said. ‘The police—’

‘I will not hide from the police. I am innocent!’ cried Vitale.

‘Innocent of what, Leo?’ asked Fortuny.

‘How precisely did you arrive in the Cavendish Laboratory, Madame?’ asked Holmes, his eyes fixed on the glamorous illusionist.

‘You must remember, Mr Holmes, I mentioned to you my friendship with a professor. I was speaking then of Cosimo.’ She took his arm. ‘He came to see our act in Birmingham, two weeks before London. After, he invites me to dinner, and—’ She smiled and took the handsome young scientist’s arm in hers. Cosimo Fortuny seemed to grow taller before our eyes as he beamed with pleasure.

It became clearer. More than a friendship, then. Cosimo Fortuny was Madame’s next ‘project’, as Holmes had predicted. Though perhaps here was the last place one would expect to find him. For a brief moment I will admit that this new mystery distracted me – distracted us all – from our dire circumstance.

‘Dinner with Mr Fortuny in Birmingham? I take it your husband was otherwise occupied,’ said Holmes.

‘The soprano,’ said Madame. ‘Remember? Touring there as well.’

‘I see.’ Holmes turned to Fortuny with one eyebrow raised. ‘Yet this is a rather fortuitious leap from your work, Mr Fortuny, to what I see here. Unless …’ A look of further understanding passed over his sharp features, and he closed his eyes, threw his head back and laughed.

‘Of course! Madame Borelli! The papers on my table at Baker Street. The ones you stole!’ He turned to me. ‘Sorry, Watson, I accused you of burning them.’

The lady smiled.

‘What papers?’ I asked. I had no idea about any of this.

She nodded. ‘Always the good ideas, Mr Holmes. Good fortune for me, as it turns out.’

‘Cosimo! What is happening here with these people? What of our work?’ Vitale nearly shouted with frustration.

‘Patience, Leo,’ said Cosimo. ‘I have loved stage magic since I was a small child. Many scientists do. I proposed to Madame and her husband that we use Geissler tubes in their act. But I was not sure how, precisely …’

‘A magic act for the music halls!’ cried Leo Vitale. ‘You trivialize our work, Cosimo!’