Beyond the window, marines continued to crunch their way across gravel, coming to the end of a path and then starting back, their swivel a rasp of stone against metal. The sound reminded Katie of her childhood. Not that she'd spent her childhood on military bases. Her father had owned a gold Dunhill lighter, the kind with a revolving pillar built into one corner. Turning the pillar made steel grind against flint to create the spark.

She'd loved that lighter.

"Tell me about your childhood," Katie Petrov said.

It was the question few clients could resist. Occasionally some patient would throw a tantrum and flatly refuse to answer, which was an answer in itself. And often Katie found herself explaining that just because something bad had happened didn't make it significant. As for the number of times ex-lovers had lain there in the dark, still burning from the afterglow, to paint the night with their when I was young...

Looking up from her sheet of paper, Katie found the prisoner staring at her. For a second she thought Prisoner Zero was looking at her breasts and then she realized, even as she blushed and grew angry with herself for blushing, that it wasn't her breasts which interested him but the 2b pencil in her hand.

"You want this?"

The pencil was entirely black, little more than a stub, with "Calvin Klein" written in script down one side and a black rubber at the top, slightly chewed.

"From an old boyfriend," she said. "A fashion journalist. We didn't last long." Men talked about themselves when they felt insecure, women when they were at their most confident. And Katie worked on the basis of information exchange; not everyone in the profession approved but it worked for her.

Prisoner Zero's eyes never left her hand, his gaze animal and hard. Working in prisons had taught Katie that almost anything could be used as a weapon. This was why her pencil was short and blunt. Too short really to hold properly, which made the thing too short to be used as a weapon. At least Katie hoped so.

"You want it?"

The man nodded.

"Then say so."

Prisoner Zero transferred his gaze from her hand to her face. He looked younger than she'd been led to expect and strangely vulnerable now that his beard and tangled hair were gone. It was hard to reconcile him with the bug-eyed fanatic featured on the front of every paper.

"Say yes," said Katie, "and you can have it. At least until the end of the session."

The man simply stared at her.

"I know you understand."

Holding out his hand, the man waited. And Katie had to force herself not to gasp at the lacerations across his palm.

"They did that to you?"

Was that a shake of his head? Katie Petrov wasn't sure. All she knew was that the man's hand remained out and his gaze had returned to the pencil.

"Okay," she said, "why not?"

Prisoner Zero tore the pencil's eraser from its sheath with his teeth and bit flat its hollow black tube. Then he ripped open the front of his orange jump suit, slid his arms from the sleeves and began to drop his trousers.

"What are you--?" Katie was about to hit the attack alarm she'd been given and which hung on a paper ribbon around her neck, when Prisoner Zero sat down again and began to use the flattened metal tube to scratch rapid lines into his thighs, blood beading the middle of the lines where his improvised blade dug deepest.

When the map was finished, Prisoner Zero flipped round the pencil, sucked blood from the edge of the metal and then used the pencil's point to sketch an identical map on the inside of his jump suit. Only then did he stand up, almost as if nothing had happened, and shuffle his arms back into the sleeves.

"Put it on the desk," said Katie. "If you've finished with it."

So he did, placing the pencil parallel to the edge, with its blunt lead just touching the corner of the manila file. This was to stop the pencil from rolling away. The ripped-free eraser he balanced on end just below the point of the pencil, like the dot on an exclamation mark.

Katie now knew three things about Prisoner Zero. He manifested self-destructive tendencies, he was anal, in the broader, less accurate sense of being meticulous and he was uncircumcised, which was definitely culturally counter-intuitive. He was also either unashamed of his nakedness or oblivious, because nothing in his recent behaviour suggested exhibitionism.

Actually, Katie knew four facts, although it took a few seconds for her memory of the needle's spoor to sink in. He'd been a drug addict at some time in his life, which undoubtedly meant he had a previous criminal record. And that should make it marginally easier to pin an identity on the man.

"I've been told you speak English," Katie said. "But if you're not comfortable with that then I also speak French and a little Arabic..."

Nothing. Just those eyes, as empty as deep space.

"You've lived in the US?" Katie Petrov glanced at her notes from habit and remembered they were blank. "Nationality?" she wrote at the top, adding her question mark as an afterthought.

"Tell me about your mother."

No answer.

Prisoner Zero watched while the woman made a note.

"What?" she asked, when she finally looked up. "Why do you smile?"

That pencil, the paper, Prisoner Zero wanted to say. He suspected, inasmuch as he thought about it, that they were intentionally old-fashioned to make him feel secure. As if a laptop might somehow be too foreign, too American.

In this he was wrong.

She'd demanded and got doctor-patient confidentiality in all matters except any directly affecting Homeland Security, which she was duty bound to report immediately, and Katie Petrov didn't want some spook with a Van Phrecker sat next door recording every keystroke she made, so she used a pencil and paper. It was her own attempt to keep the interview secure.

The first of the imperial pavilions was simpler than the servitor had expected. Still vast, but simpler. A double-eaved hipped roof rested on red walls, while fretted shutters that hinged from the top were held open by ropes, the windows below being surprisingly ordinary and papered from inside. An empty bed, built from brick and covered with a silk mattress, stood against one wall. The silk was crumpled and scrolls lay unopened next to it on the floor.

A Tartar bow and a quiver full of arrows gathered dust on a gable high overhead. Not having seen a bow before, the servitor imagined it was some kind of single-stringed musical instrument.

The tray was his passport through the pavilions of the inner court. An ebony and jade passport laid with a glass cup, squat iron teapot and pre-warmed gold platter on which sat five types of dim sum, each one representing all that was best of the cuisine of the original Middle Kingdom.

Sous Chef Chang San had been careful to tell the servitor the significance of each morsel and how it related to the others on the plate. As well as jiaozi dumplings, Szechwan huntun and char siu bao (steamed buns with roast pork), there was har gao and, obviously enough, the sous chef's special pork dumplings.

The young man doubted if the sous chef really expected him to explain this to the Emperor. Failing that, however, there seemed little reason for Chang San's manic intensity or the way he demanded the servitor repeat back the descriptions to prove that he knew which of the slowly congealing lumps of food was which.

"You won't forget?"

"Of course not."

Chang San smiled thinly. "Be sure you don't." He wouldn't put it past the young man to claim the cooking as his own. There was something untrustworthy about the servitor's eyes, which were much too wide apart and possessed an unsettling insolence. Worse than this, his nails were filthy and Chang San found it hard to believe that any previous emperor would have been willing to take food served by someone with dirty hands.