'He could be working as part of a gang,' I said.

'Unlikely,' Holmes snapped. 'Remember William of Occam's suggestion that one should not multiply logical ent.i.ties without reason. No, for the moment we will a.s.sume that our man is working alone.'

'Is your Doctor a tall chap with a shock of white hair and a penchant for velvet smoking jackets?' Mycroft asked.

'No,' I said, mystified. 'Why?'

'There's a chap who I see down in the reading room sometimes, calls himself the Doctor. Thought it might be one and the same. This one's a bit of a wag: brings newspapers into the Club dated some ten or twenty years hence and reads them as if he'd never seen them before. Got some of the members quite worried, I can tell you.'

'Apart from the coincidence in names,' Holmes said, leaning forward and fixing his brother with a hard stare, 'is there any reason why he should be the same Doctor?'

'Well spotted, Sherlock. I do have a reason. You see, a good half of the people on this list are members of the Diogenes!'

Holmes stood bolt upright, and I must admit that I was taken aback. The entry requirements for the Diogenes were notoriously stringent. To find that many of our suspects were regularly gathered together under one roof . . .

'Who?' Holmes asked succinctly.

'If we ignore the Doctor, then Challenger, Baron Maupertuis and. .'

Mycroft trailed off. Holmes nodded. I felt completely left out. There was a name on the list that was being kept from me.

Mycroft Holmes pulled a discreet velvet cord, and within seconds a footman had entered the room. Mycroft murmured a few words, and the man left.

'I have asked Baron Maupertuis to join us, if he is on the premises,' Mycroft informed us.

'What sort of a man is he?' Holmes asked.

'A strange sort,' Mycroft replied. 'Rich - exceptionally so - and a bit of a recluse. He is of Dutch extraction, and owns the Netherlands-Sumatra Company, but has recently become a naturalized British subject. Seems to be trying to be more British than the British: friends with the Prince of Wales, goes to Ascot, you know the form. We suspect that he is mixed up in some shady business deals, which is why we encouraged him to join the Diogenes.'

'Because you wanted his help?'

'Don't be clever, Sherlock. We wanted to keep an eye on him.'

As we waited, Mycroft poured me a gla.s.s of heavy, sweet sherry, and made small talk about the weather. He was not very good at it and I was glad when the door reopened.

The man who walked into the room was tall, excessively so, and thin to the point of emaciation. His face was bloodless and completely without expression - so immobile, in fact, that it could have been carved in bone.

His hair was long, ash-blond and brushed straight back: the irises of his eyes were so pale as to be almost invisible, so that his pupils were black pinp.r.i.c.ks floating on a white void. His morning attire was impeccable. He did not offer to shake hands.

'Mycroft,' he said finally. His voice was like the wind in dry reeds. 'I trust that this is important. I have another appointment.'

'I wished you to meet my brother, Sherlock,' Mycroft said. I could tell that even he, the imperturbable Holmes, was put out.

Maupertuis's gaze settled on Holmes and he nodded slightly. Although his expression did not change by one iota, something new had been added to the atmosphere of that room, an indefinable but ominous cloud.

'Charmed,' Holmes said, sniffing slightly. 'I was saying to my brother only a moment ago that we both belong to the same library.'

Maupertuis said nothing.

'A library in Holborn,' Holmes continued.

No reaction.

'I don't remember ever seeing you there. Do you go often?'

Maupertuis reached a skeletal hand into his waistcoat pocket and retrieved an ornate gold hunter, which he consulted. I noticed that the rest of his body did not appear to move at all. He swivelled slightly so that he was looking at Mycroft.

'Time presses,' he whispered. 'You understand.'

He turned to go, and as he did so, his gaze swept across me like the beam of a lighthouse. I felt as if insects were crawling across my skin. The feeling lasted but a moment, and then he was gone.

'He did not blink,' Holmes said finally. 'Most instructive.'

'A rum character,' Mycroft said. There was a fine beading of perspiration across his forehead. he took out a handkerchief and mopped it abstractedly across his face. 'I've never got his measure.'

'I wonder whether his appointment was real or feigned,' I said. 'It occurred to me that he might have wished to avoid further questioning, and invented a spurious excuse to leave.'

Holmes crossed to the window.

'We may be able to tell something by the way he . . . ah! Yes, there he is now, climbing into a hansom.'

Holmes suddenly leaned forward, like a pointer dog on the trail of a stag.

'h.e.l.lo, what's this!'

Mycroft and I moved to join Holmes. Mycroft, being nearer, got to his brother's side first, effectively blocking my view.

'Most instructive,' Mycroft murmured.

'You noticed?' Holmes. said.

'Of course.'

'What's happening?' I bleated.

Mycroft moved aside and I squeezed past him to gaze along Pall Mall at a swaying two-wheeler with a baronial crest upon its side.

'I see nothing,' I said.

'You see nothing now,' Holmes corrected. 'The hansom was listing sideways before Maupertuis entered. His weight evened the suspension out.'

'I don't . . . Ah! I see! You suspect that the hansom was already occupied?'

'I suspect nothing,' Holmes replied. 'I know. The science of deduction allows no room for suspicions. A fact is either true or it is not true. Did you not notice how Maupertuis was in a hurry to leave us for another engagement? I would suggest to you that he was due for an a.s.signation with another person. The coach is obviously his, judging by the crest, and contains the person with whom he is meeting.'

It would be instructive to know the ident.i.ty of the other man,' Mycroft said ruminantly. 'Save that he is elderly and does not often visit London, I can tell nothing about him.'

'He is of above average height,' Holmes added.

'Or thinner than the norm,' Mycroft riposted. Both brothers smiled. I was at a loss. I wanted to ask them how they could tell all this from the tilt of a hansom cab, but the answer would only make me feel a fool for not being able to tell myself.

Just then the hansom described a wide half-circle and began to trot towards the Diogenes again. As it pa.s.sed, I craned my neck in an attempt to see its occupants. Holmes and his brother had moved back into the room, and so I was the only one to see the silhouette of a hooded and robed figure sitting next to the Baron - the same figure that I had seen in the Library of St John the Beheaded.

Chapter 6.

In which Holmes and Watson make a subterranean voyage and a footman is fired. is fired.

'I need to see that man,' Holmes snapped after I had imparted the news to him. 'It may be that there is nothing suspicious in this meeting - after all, we already know that the Baron is a member of the Library. Never the less, a hooded man is a suspicious figure of almost gothic proportions. Where will Maupertuis be heading now?'

'Sherlock, I'm not even my brother's keeper, let alone that of a foreign n.o.bleman. Come, we will ask the doorman.'

Moving quickly for a man of his build, Mycroft led the way out of the Visitor's Room, along hushed corridors and down the wide marble staircase to the foyer of the Diogenes Club. Whilst we waited by the main desk, he beckoned the doorman to the steps just outside the door and flung questions at him. As he gestured to us to join him outside the club doors, I saw him slip the man a shilling.

'Jessup here says that the pa.s.senger was in shadow, but he heard the Baron tell the driver to head for an address in Euston.'

'Then we must get there before him.' Holmes looked around for a cab, but there were none to be seen.

'He has a good few minutes start,' Mycroft said. 'By the time you get there, they will have entered the house, and you may never see the other pa.s.senger. Unless...'

'Unless what?'

Instead of answering, Mycroft led us both back inside the confines of the Diogenes and through the reading room - a large, oak-lined study in whose deep leather armchairs sat a cross-section of the most important, the most unconventional and the most unpleasant men in the Empire. Skirting around the back of an armchair, I found myself looking at a familiar face.

The Doctor.

He was standing in front of the armchair. Its occupant was reading a copy of the Times. From my position behind him I could see that he was attempting to finish some kind of word puzzle - a grid composed of black and white squares into which he was inserting words. He had one set of s.p.a.ces left to fill, and from the look of him he had been stuck for some time.

The Doctor was busy writing something on a piece of paper. Seeing me, he put a finger to his lips. I looked down at the man in the chair. His hair was white and he was wearing a black velvet smoking jacket. Stumped by the clue, he rubbed the back of his neck in annoyance.

The Doctor coughed slightly. Immediately, the paper was lowered and the man in the chair glowered at him.

The Doctor held up his piece of paper.

14 Across, it read, Sesquipedalian.

'You bounder!' the man expostulated. The Doctor scurried off, grinning, and the white-haired man leaped to his feet as a number of irate footmen converged on him. I ran after Holmes and Mycroft, ashamed of the Doctor's juvenile antics.

Mycroft took us down a side corridor. A few yards along it was a door marked Billiards Room.

Mycroft took a key from his waistcoat pocket and unlocked it, then led the way inside.

Excepting a billiards room, I was taken aback to find a gas-lit and carpeted stairway. I stumbled down the first few stairs into Holmes's back. In front of me, over Holmes's head, I could see Mycroft's huge bulk filling up the s.p.a.ce from stairs to ceiling and from wall to wall. As we walked I wondered what would happen if he got stuck.

How could we get him out? Thank G.o.d he was in front, otherwise how would we get out?'

We walked on, and on. The stairs led down, seemingly to h.e.l.l itself. A sudden whoosh in the distance made me jump. Seconds later a warm breeze caressed my face.

'Where are we going?' I whispered to Holmes.

'Hanged if I know,' he replied over his shoulder, 'but I doubt that it's the wine cellar.'

Light blossomed around the edges of Mycroft's body and within seconds we were standing in a s.p.a.cious, bricklined cellar from whose ceiling an incongruous chandelier dangled. Looking back up the stairs, I could see a glimmer of light. The distance was not as great as I had feared. Relieved, I looked around.

Comfortable sofas lined the walls, and tables held copies of the day's newspapers, but my eyes were caught and held by the semicircular cast-iron object which protruded from the far wall. It was about four feet across and festooned with a number of smaller pipes, one of which seemed to have a knurled wheel attached. I moved closer. It appeared to be some form of hood and, kneeling and gazing into it, I could see that it was the final few feet of a tunnel. The rest of the tunnel, which was lined with cast iron, vanished into darkness after a few feet. A large hatch, hinged at the top, hung over the opening and two rails, about three feet apart, emerged from it and crossed the cellar almost to where we stood. Sitting on the rails was what I can only describe as an large artillery sh.e.l.l on wheels.

'Barker?' Mycroft roared. We were obviously in another part of the Diogenes Club in which speech was permitted.

'Ere, Guvnor!'

A small man emerged from the tunnel. His skin was pale, his eyes dark, and he was dressed, incongruously, in immaculate morning dress.

'Be wantin' a trip, will ya?'

Without waiting for an answer, he threw some kind of catch and opened the entire top of the wheeled sh.e.l.l. The interior was padded with velvet and contained two small armchairs.

'All aboard that's goin' aboard,' he said.

I looked questioningly at Holmes. He, in turn, looked at his brother.

'Get in,' Mycroft said. Holmes shrugged, and did so. I, with some trepidation, followed.

The armchairs were a tight fit. I gazed up out of the sh.e.l.l at the chandeliered ceiling.

'A pneumatic railway built for the Post Office and first used in 1863,' Mycroft explained, beaming down at us. 'They used it to move post from Euston to the General Post Office at St Martin's le Grand. They abandoned it in 1880.

The Diogenes bought it - through one of our members, of course - and extended the line to here. Excess air pressure - provided by the London Hydraulic Power Company from their pumping station in Pimlico - pushes the sh.e.l.ls along, and a partial vacuum in front of them aids the process.'

'For what purpose?' I gasped.

'To get people in and out of the building un.o.bserved,' Holmes said. I could tell from his tone that he, too, felt a modic.u.m of discomfort.

'Quite right,' Mycroft said. 'Certain meetings held on these premises have quite distinguished guest lists. It would not do to have them observed.

And...' his voice hardened,'... it would not do to have any mention of this private railway in the public domain. It shall remain our little secret.'

He made a signal to Barker.

'First stop Euston, a short walk away from Drummond Crescent, where Baron Maupertuis is making for. Pleasant journey, gentlemen. You will forgive me for not joining you.'

The lid came down.

'If anybody had told me this morning,' I said with some venom, 'that I would be shot like a bullet beneath London before lunch, I would have called them a liar.'