'Ridding your mind of that which you value most was the hard bit,' replied the woman. 'All I had to do then was to invoke your dread, the memory that you feared the most. After that, it was easy.'

'My greatest fear?'

She smiled again and showed me the hand mirror. There was no reflection, only images that flashed past anonymously. I took the mirror and peered at it, trying to make sense of what I saw.

'These are the images of your life,' she told me. 'Your memories, the people you love, everything you hold dear – but also everything that you've ever feared. I can modify and change them at will – or even delete them completely. But before I do, I'm going to make you view the worst once more. Gaze upon it, Thursday, gaze upon it and feel the loss of your brother one last time!'

The mirror showed me the image of a war long ago, the violent death of a soldier who seemed familiar, and I felt the pain of loss tearing through me. The woman laughed as the images repeated themselves, this time clearer, and more graphic. I shut my eyes to block the horror, but opened them again quickly in shock. I had seen something else, right at the edge of my mind, dark and menacing, waiting to engulf me. I gasped, and the woman felt my fear.

'What is it?' she cried. 'There is something I have missed? Worse than the Crimea? Let me see!'

She tried to grasp the mirror but I let it drop. It shattered on the concrete floor and we heard a muffled thump as something struck the steel door five storeys below.

'What was that?' she demanded.

I realised what I had seen. Its presence, unwelcome for so many years in the back of my mind, might be just what I needed to defeat her.

'My worst nightmare,' I told her, 'and now yours.'

'But it can't be! Your worst nightmare was the Crimea, your brother's death – I know, I've searched your mind!'

'Then,' I replied slowly, my strength returning as the woman's confidence trickled away, 'you should have searched harder!'

'But it's still too late to help you,' she said, her voice quavering. 'It will not gain entry, I assure you of that!'

There was another loud crash; the steel door on the ground floor had been torn from its hinges.

'Wrong again,' I said quietly. 'You asked it to attend, and it came.'

She ran to the stairs and yelled:

'Who is there? Who are you? What are you?'