‘That one!’ cried Fortuny, pointing to a second cupboard at the back of the lab near the sink. Holmes ran to it and threw open the door. There was room inside, in front of some crowded shelves.

At the same time, the senior scientist dashed to the end of the lab near the door, to fire up the Ruhmkorff coil.

‘Down here!’ I heard a familiar, gruff voice in the hall outside.

‘Holmes! It is Pickering,’ I whispered.

Holmes grabbed my arm, pulling me into the cupboard. ‘Mr Vitale, you too – inside! Mr Fortuny, work your magic. Not a word, Madame! Hurry!’

But Leo Vitale pulled away.

‘Vitale! Come!’ Holmes grabbed Leo Vitale’s cuff, but the young man yanked his arm free.

‘No! I am innocent. I will face the police!’ he cried.

‘They will not believe you,’ said Holmes. But the young man moved out of reach.

We heard noises at the door of the laboratory, and Holmes and I ducked back into the darkness, closing the cupboard door in front of us, leaving only a crack. We were concealed but could see what was going on in most of the room.

Fortuny, down at the end near the door, doused the lights. In the dimness I saw him pull a large-handled lever near the Ruhmkorff coil. There was a hum, then a sudden loud crack as a bolt of miniature lightning arced between two metal poles adjacent to the black tube. A sizzle sounded, then a hiss of gas as the tubes slowly swayed gently in their wire cradles fastened to the wall.

Fortuny threw another switch. All along the walls the small sausage-like tubes suddenly lit up in glowing, ethereal greens, reds and blues. He ran past us and took up a position with Leo Vitale behind us, at the darkest end of the room.

‘Fantastic!’ whispered Holmes. It was indeed a strange and marvellous effect.

Just then the door burst open and silhouetted against the light in the hall were Pickering and two constables. The flicker of the glowing coloured lights danced in patterns across their surprised faces.

‘What the devil is all this?’ boomed Pickering. ‘Light the lights, someone!’

Madame Borelli now emerged into our view as she walked past our hiding place and the glowing tubes, slowly towards the door where the police stood. Her arms were outstretched, as if in a trance. She spoke in a deep, otherworldly monotone.

‘Welcome to the humans. Beware, beware! I summon the spirits,’ she intoned. ‘I call forth here, the powers of the dead – to come, to come … and to change the energy of this room …’