When he looked up again only the skyboarder remained, as something dark disappeared out the broken window and the other was set to follow.

"Watson, grab her."

The sparking compudroid looked up slowly and reached out, locking a hand round the ankle of the skyboarder. Immediately she was kicking, howling and screaming like something possessed, but nothing could make Watson let go. As Holmes came within range she lashed out with a fist which he caught easily.

"I suggest that you calm down, madam; Watson, damaged as he is, will not let go of you until I say otherwise, and your friend is long gone by now."

Hollow laughter verging on hysterics erupted from behind the helmet. "Friend. You call that creature a friend of mine. But you're right; I have no chance of catching him in the fog now, Mr Holmes, and I hold you entirely to blame."

Holmes smiled coldly. "It was you who knocked me out of the way, madam."

"Ah, but it was your stupid droid who prevented me from chasing him. I could have caught him even in this fog; I could have made him pay for what he has done." The figure was shaking now.

Holmes let go of the fist. "Do you know what will happen to Lestrade, madam?"

The figure shrugged. "Hard to say; maybe he will kill her outright. Maybe he will keep her as a bargaining card, as he told you he needs your brains." The figure straightened. "Yes, he must come back for you; all is not lost. Mr Holmes, you have no reason to trust me, but you must believe me when I say you and all of your friends are in the most terrible danger. If you will release me so I can examine your droid I will tell you about the worst man in London and perhaps a little of my own story as well."

She could see the wary glint in his eye. "If you do not trust me, Mr Holmes, put the skyboard at the other end of the room behind a chair or something. I cannot leave without it."

Holmes picked up the board and slid it under a chair. "Watson, you can let her go now, old fellow."

With painful slowness the compudroid released his grip on her ankle, and immediately she moved over the fallen droid and opened a panel in his back. Removing a small tool from her back pocket, she set to work. Holmes righted an overturned chair and sat down. Already the blue sparking that was covering Watson had faded; little bolts of electricity jumped under the tool.

"And now, madam, if you would be so kind as to remove your helmet and tell me why my friends and I are in such deadly peril?"

The figure paused from her work and stared at him before slowly flicking open the catches that held her helmet. As she removed it Holmes saw a young face with two blue eyes emerge followed by tumbling brown hair, but it was the black mask that covered the right half of her face that held his attention. She pulled her hair forward to hide it.

"I see you used to be a professional skyboarder."

The blue eyes registered surprise. "Yes, I gave it up a few months ago. How did you...."

Holmes smiled. "You have had the racing logos and sponsors removed from your suit; in the right light you can still make out some of the names."

"I might have guessed it was just trickery, Mr Holmes." She picked up the tool and made a few minor adjustments to Watson before closing the panel. "He'll need to be taken down to a beater's at some point to get the dents out of the body but he won't explode or anything."

Watson stood up and flexed his hands. "Sorry I wasn't much help, Holmes."

"You did more that you realise by catching our guest here."

The woman glared and moved over to the army droid; flicking open a panel she ripped out a few internal wires and removed a blue clip from its head. "You have no idea how much it costs to get hold of one of these things," she explained, sliding the clip into a side pocket.

"And now for the explanation I see you are most eager for, Mr Holmes; if Watson would care to sit down I will explain as much as I can. My name is Tessa Louise Moriarty."

Holmes flinched and Watson made a gasping noise.

Tessa raised her hands. "Please, I will explain. Professor Moriarty, the one who is terrorising London at the moment, is a clone of my grandfather of so many greats I don't care to recall. In his youth in Victorian times he had a son, one Edward Moriarty, with an actress who died young; and Edward, as far as I can make out, was left in the care of a relative. The name has passed down to me over time. From Edward onwards, most of us have been law abiding citizens. There have been no more master criminals, no more need for dramatic deaths in waterfalls; we have lived quietly, the name gradually dwindling down to my father and now me. I am the only Moriarty who should be alive in this century." She paused and stroked the mask under her hair.

"My commiseration on the death of your father, Miss Moriarty."

She looked up and took the hand away from her face. "Ah, yes, another trick, I said 'I', not 'we', yes. Four months ago I was asleep in my parent's home when a fire broke out -- deliberate arson I was told afterwards. Only I escaped, by some miracle, alive but not unscathed and with a burning desire for revenge." She sneered. "The new Professor Moriarty sent people to 'collect' me from hospital. I spent two agonising weeks with him picking my brains over every detail of the fire before giving me money for reconstructive surgery and telling me to leave." She rubbed an eye with the back of a gloved hand.

"I donated the money to some charity or other, and began to find out things on my own. I'm not as stupid as he thinks I am, and I began to learn things here and there, a long and painfully slow process. Moriarty hasn't been doing as well as he wants people to think. At the moment he's trying to regain his old territories and is in a bitter gang war with a group called the Scar, and he's only just winning. I don't know why as yet but it seems someone in Scar has hired a murderous dog called the Shadow to wipe out Moriarty. Unfortunately for my family, Scar also thought it might be better to unnerve him with a warning first."

Holmes had his hands resting against one another and was watching her intently. "Your family."

"Yes, my family. Not even the dog was safe; it had been shot to stop it barking. And now the Shadow is ready to kill Moriarty, but he needs your help to do it; he needs your knowledge of the man and his methods in order to get close enough. After he has finished with you and your friends, none of you will ever be found again."

Holmes got up and produced a white handkerchief from deep in a pocket. Tessa took it and dabbed her eye in surprise; she hadn't even realised she had been crying.

Holmes went into a back room and came back carrying a bag. "Watson, go and pack whatever you need for a short trip."

"Where are we going Holmes?"

"Anywhere but here. Hurry, man. I'll phone the police and explain about the droid and also find out if Lestrade's really gone."

Tessa stood up from where she had been crouching by the army droid. "There's an empty room opposite me; it would be easy enough to break in and cheap enough if you wish to pay." Tessa picked up her helmet and began to flick the clips into place. On stamping the heel of her foot against the floor, the skyboard slid out from under the chair and skidded to a halt beside her. "I suggest a taxi; your car is too noticeable."

Holmes stopped dialling. "You've been watching us longer than tonight."

"Just about over a week now."

"Let me guess: long black wig, faded jeans and a blue top."

"When did you see me?"

"Yesterday!"

Under the helmet she smiled. "Ah, yes, the shopping arcade."