Romana sighed. 'What do these inscriptions say?'

'"When thunder wakes people a hundred leagues away, you shall lose neither ladle nor spoon." '

'If you can't read the ideograms, just say so.'

'I can't read the ideograms. The two outer rings are some kind of astrological data, the next one is geographical direction and the next two relate to landscape features. What do you think, K9?'

K9 scanned both lockets with his extendible probe. 'Blood is Type AB and bears the same genetic code as the hairs in the car I scanned at Nang Tao airfield.'

'Blood?' the two Time Lords echoed. The Doctor turned the locket around in his hand. 'What blood?'

'The ideograms are inscribed in blood, and have then been varnished over,' K9 explained patiently. Yeung wasn't surprised; the Tongs demanded palpable displays of loyalty.

'Is this from the same person as the blood on that knife?'

'Negative. Chemical and hormone balance suggests this sample is from humanoid female of approximately twenty-two years of age.'

'Hmm. Hunting trophies, probably.' The Doctor dropped the locket absently into a pocket.

Romana discarded the other with a distasteful look and searched her nearest a.s.sa.s.sin for anything he might have in his pockets, but the plain black clothes didn't seem to have any pockets. There was, however, a mark showing from under the sleeve of his right arm. She pulled back the sleeve to reveal the sinister black and red tattoo of a scorpion, its stinger uncurled to strike. 'Have you seen anything like this before?'

The Doctor looked, his face hardening. He let out a long sigh. 'That explains a lot.'

'You know about it?'

'Yes. It's a Tong sign: the Black Scorpion, from the western mountains of Sichuan.' He led her out of the cell and locked the door. They went into the main office where the Doctor set about recovering the rest of their belongings from the cabinet in which they had been placed.

'They're a criminal organization?'

'They're the the criminal organization, second only to the Lascars in the Si-Fan. When the Manchu dynasty usurped the empire from the old Ming dynasty in the seventeenth century, a lot of the old Hung secret societies reformed to resist them. criminal organization, second only to the Lascars in the Si-Fan. When the Manchu dynasty usurped the empire from the old Ming dynasty in the seventeenth century, a lot of the old Hung secret societies reformed to resist them.

Eventually they evolved into the Tongs and Triads. The Black Scorpion in particular are devotees of an ancient G.o.d called Weng-Chiang.'

'Three hundred years isn't very ancient.'

'No, well, obviously the Tong was formed from bands of Chinese dacoity that had been hanging around the mountains since before Qin Shi Huangdi unified the empire way back in the third century BC. Like the Thuggee in India, they committed acts of banditry on behalf of their G.o.d.'

'This Weng-Chiang?'

'Yes. He's an ethnic corruption of Sung-Chiang, the G.o.d of thieves and criminals. He had a thousand names and could take on any appearance he desired.'

'It doesn't sound like a good role model to me.'

'No... In his form as Weng-Chiang he could kill with light from his eyes and had absolutely lethal halitosis.' Finally settling his scarf into a comfortable position, he crossed the office to peer out of the main doors of the station. 'The coast looks clear; let's get out of here.'

'Right.' Romana bolted for the door but was quickly held back by the Doctor.

'Not like that! You obviously haven't escaped from many jails. If people saw us running away, they'd think we're fugitives, as opposed to travellers strolling out after asking directions or reporting a missing dog.'

'Oh, I see. Sorry; but I didn't tend to get locked up until I met you.'

'Is that my fault?' Shaking his head, the Doctor strolled casually out the door.

Professor Ying shook his head as Li left; people just didn't use their heads enough, in his opinion. Knowledge was man's greatest weapon, he had always felt. He put down his cup and picked up the knife. He had a suspicion that had been nagging at him all along and wanted to test his theory in private. He held the knife pressed against the hot side of his tea urn. After a few seconds, the blade spread outwards in the blink of an eye.

Ying smiled to himself; it was exactly as he had expected.

He lifted the office telephone and dialled. 'Get me the Kuomintang barracks for the Fourteenth Engineers; the commandant's office.'

Yan Cheh was surprised to see the two westerners leave the police station so soon. He had discarded the leather coat and motorcycle goggles in favour of a loose suit and slouch hat since he had brought a car this time.

There was a strange machine with them vaguely doglike, but all metal. Yan Cheh had never seen such a thing, though he supposed it was some American, or perhaps German, motorized contraption.

Together, they were all hurrying off through the street, dodging hawkers every foot of the way. Starting the car an old Bugatti Yan Cheh followed them at a mere walking pace. His slow speed was hardly unusual, given the number of people walking or just standing in the middle of the road.

Li's easy smile had returned as he took the stairs back up to ground level. At least he could go on holiday having got a good result. His smile froze as he entered the empty office, noticing both the main door and the door to the cell area ajar.

He bolted across to the cell area and was rea.s.sured to see that all the doors were still locked. Less rea.s.suring was the sight of the various weapons lying around the floor. Drawing his gun, he advanced into the corridor. Each cell had its inmate safely ensconced within, all looking strangely amused though they all remained silent.

He reached the Doctor's cell and was dumbfounded: it was full of unconscious Tong footsoldiers. Perhaps Du had gone over his head, he thought, and decided to deal with the strangers in his own way. If so, not only was it insulting but also a failure. He checked the men's wrists to be sure and was surprised to find that they wore Black Scorpion tattoos like the coolies from the opium den. A locket was lying on one of the rec.u.mbent bodies, and he examined it, seeing immediately that it was a geomancer's compa.s.s. Slamming the cell door in disgust, he crossed to Romana's cell, then slumped dejectedly against the door. He had the nasty suspicion that his head would roll if his superiors ever found out that his men were now locked in there.

Yan Cheh followed the strangers all the way back along Bubbling Well Road and round the corner to the Waibaidu bridge. To his surprise, the man was unlocking the door of a large blue booth, and all three entered.

Yan Cheh examined it from the other end of the bridge: it proclaimed itself to be a police telephone box of the kind they had in Britain. Perhaps the British had imported it for the Settlement Police. If so, then the fact that the man had a key to it suggested that they were something to do with the Settlement Police as well; investigating the local force, perhaps.

Perhaps they were also friends of the Fallen Angel and were following their shared mystery back to its source. Yan Cheh turned round in his seat, switching on a field radio that was built into the car's rear bulkhead and took up most of the boot. 'Rondo; it's me. Look out the recordings of Du's visits. I think we may find it useful to drop some hints to certain people.'

Six.

Inside the TARDIS, the Doctor tossed his hat casually onto Ithe hatstand. 'Romana, there's something very odd going on here.'

'Someone must be tapping the powers of the fourth segment the way that boat appeared... It seems a logical enough hypothesis. The last segment was being used to move between normal s.p.a.ce and hypers.p.a.ce.'

'Yes, so you ' The Doctor froze, open-mouthed.

'Waitwaitwait... Wait a moment. Just what is it that the tracer traces? Hmm?'

'The segments of the Key '

'Ah, but how does it recognize a segment, eh? What are the preprogrammed triggers that it reacts to, eh?' He gave Romana a wide-eyed look of encouragement.

'Any substance with a variable atomic weight; there can't be too many of them around.'

'And?'

'And...the segments all have the powers of trans.m.u.tation and transmigration.'

'Think, Romana; we're looking for the Key to Time, right?

If it has any energies useful in the control or manipulation of time '

Romana straightened abruptly. 'The segments must be charged with chronon energy! You mean the tracer could be reacting to chronon radiation from another source?'

'Exactly. If there was a large enough energy source intersecting a temporal shift in the vicinity it would give off more chronon radiation than any of the individual segments.'

His tone darkened. 'The big question is: what energy source, and what temporal shift?'

'Surely that can wait until we've completed our mission?'

'I doubt that. So long as the source of chronon radiation is still operating, the tracer will just keep on reacting to it and bringing us back here. Unless, of course, you're confident enough about your understanding of Guardian technology to reprogram the tracer to screen out the chronon radiation.'

Romana gave the tracer a wry look. 'I wouldn't think so.'

'Neither would I.' The Doctor rubbed at his chin. 'On the other hand, what if we were to make a dedicated chronon detector? The tracer's only picking them up as interference among a variety of signals, but a dedicated sensor wouldn't have all that nonsense to worry about.'

'K9's sensors?'

Both Time Lords looked at the mechanical dog. The indicators on K9's input panel flickered through a diagnostic cycle. 'Master; paralleling my neutrino converter with a tachyon resonance filter will perform the required function.'

The Doctor and Romana knelt beside him. 'Brilliant!' the Doctor shouted, making Romana wince. 'Any difference in background neutrino levels or velocities will be the result of interference from the chronon discharges. The filter will a.n.a.lyse any of those resonance anomalies and give us a read-out on chronon strength and location.'

Romana brushed a strand of dark hair away from her eyes.

'I suppose you want me to say that's terribly clever.'

'Well, I'll take any complimen'

K9's tail wagged slightly. 'Congratulations are unnecessary, mistress.'

The Doctor's face fell.

HsienKo emerged into the wide hall of her house from the nursery. Like so many European mansions, the hall contained a wide staircase rising from a chessboard-patterned floor. A few statuettes of local deities and dragon kings were dotted around on low pedestals.

Kwok had been waiting patiently outside. The right side of his face was pink and scarred, but he now wore a patch over his burnt eye to hold on a white disinfectant pad. Even with only one eye and a morphine-blurred mind, he could see that something affected her when she was in there. She didn't look hurt as such, but perhaps slightly lost. She composed herself quickly, and beckoned Kwok. 'I'm concerned about the effect that losing the opium den's altar will have on the Tong. Most of them honestly believe that their faith will bring back Weng-Chiang.'

'Their belief can't hurt our plans.'

'No, but it may blinker them to other events around them that could. Religion seems to do that. You'd better go back and recover the altar; we might need it for the troops' morale later.'

Kwok nodded impa.s.sively. The beliefs of the Tong's footsoldiers didn't mean anything to him, but morale was something he could understand. 'Consider it done. There is one other thing...'

'It won't be much longer until you can retire.'

'I've been thinking that for years.'

'This time it's true. We already have the moderator in place in the core cavern.'

'Then we'll need more power conduits.'

'I'll find a suitable target.'

His subordinates had delivered their reports on the interrogations of the prisoners from the opium den, but Inspector Li didn't think much of the answers. Everybody seemed to have developed acute amnesia that even the occasional pistol-whipping couldn't cure.

Forensics had turned up nothing at the shrine in the back room, and its presence was just about the only thing he had which provided a clue. If he knew which G.o.d it was dedicated to, he might be able to work out which group were followers.

Unfortunately, there was no sign of sacrifices or offerings that Ying had been able to identify. Most G.o.ds didn't require blood, of course, but Li had thought it would have been conveniently memorable if this one did.

The shrine had been built into the wall, he recalled. Perhaps there was something hidden behind it. It couldn't hurt to look, he decided, and he didn't have much else to go on. He called out to a uniformed officer who was pa.s.sing his desk. 'You!'

'Yes, sir?'

'Get down to Ying, and tell him to prepare for a little expedition.'

The Doctor knelt beside K9, his head and hands buried inside the robot's glittering innards. Romana was examining the tracer for any signs of damage it might have received lately.

The sonic screwdriver buzzed, and there was a flash and a bang from inside K9's casing. The Doctor hurriedly straightened, blinking rapidly, and peered at a charred circuit in one hand. 'Hmm. I wonder what that was for.' He tossed the circuit over his shoulder. 'All right, K9, what about now?'

K9's antennae wiggled with a whirr. '11101001010001 '

'Stop!' The Doctor picked the discarded circuit up off the floor and blew some dust off it. 'So that's what it's for.' He hastily repaired the damage and squeezed the circuit back into place. Right. How about that?'

'Translator unit functioning normally.'

'Yes, yes, I can hear that, but what about the resonance filter?'

'Modifications are adequate. I am detecting latent chronon decay in several locations.'

'Several?' Romana asked.

'Affirmative, mistress. Correlation of available data suggests a network of locations recently exposed to chronon radiation extending beyond sensor range.'

The Doctor sealed up K9's inspection hatch and wiped his hands on the end of his scarf. 'I don't like the sound of that.

We have to find out what's causing it.'