"Yes," says Holmes, to himself and not to me, I realise, "I believe we've been standing out in the rain for long enough."

Holmes is flat against a brick wall, breathing hard and utterly soaked. We both are.

"Long enough for what?" I ask.

He smiles superciliously, and it takes some effort for me not to throw a right hook. "Time for tea, Watson?"

"Tea?" I ask, my incredulity yet to wane in the face of such bizarre behaviour. "Tea!" I repeat, turning to anger. "Yes, I'd like a b.l.o.o.d.y cup of tea. An hour ago might have been nice."

Holmes smiles again. "Tea it is then." He proceeds to slap me on the arm as he sets off at a brisk pace in the direction of our by-now-distant lodgings. "Come now, Doctor, you'll catch a death out here in this rain."

He is fortunate I am tired and a few paces behind, or I may well have thrown that punch after all.

But as we walked back to Baker Street like two drowned rats, I wonder what has set him off; what has arrested Sherlock Holmes' senses to make him wander off and take such a circuitous route back to our abode? If I didn't know any better I would say he is trying to discern if someone is following us. I look back on several occasions but see nothing out of the ordinary. In a city like London, with its black, beating heart, there is no shortage of ne'er-do-wells, ruffians and a.s.sorted vermin that would do well-heeled, law-abiding folk harm. I see plenty of these but none whom I believed Holmes would regard as a threat.

It is with grateful eyes, then, that I finally behold 221b Baker Street and imagine the warm welcome we will receive within.

Still, the chill that something or someone has alarmed my colleague persists even after the fire is lit and a hot towel is curled around my shoulders. It is to be as nothing to what we will encounter later.

"What are you looking at, Holmes?" I ask, mildly exasperated. I have a small gla.s.s of whisky in my left hand, a cigar in my right and am warming my bare feet on the fire. I have changed my clothes, dispensing with my sodden garments for Mrs Hudson's expert attention. The towel around my shoulders is warming my neck and I sit in a plush armchair, glad to be out of the storm lashing the streets outside.

Holmes is transfixed on the gloom below our window, staring seemingly without blinking at some unknown and unseen terror only he can perceive.

He doesn't answer.

"Holmes, you are soaked and will catch a death of cold if you do not change. At once, old boy, doctor's orders. I insist."

"Watson," he replies, "you are as badgering and ineffectual as our old nanny. Mrs Hudson has tried, and failed, to dislodge me. I shall not be moved."

"At least take a towel, Holmes, or remove your jacket. I have no wish to be ministering to a dose of influenza because of your recalcitrant att.i.tude."

"On the contrary, Watson," he corrects me, unflinching in his dedication, "it is essential."

I decide to drop the matter. In a battle of wills, I am wise and humble enough to accept that Sherlock Holmes would always be the victor. Instead, I cast my mind back to the alley and that scene of utter horror and bodily devastation.

"What manner of man could do something like that?" I wonder out loud. "How," I say, turning away quickly from the fire to regard my colleague again, "could a man possess the strength to remove another man's head, and why?'

"I feel it is connected," says Holmes.

"Is that a joke?" The seriousness of my colleague's expression suggests it is not. "Connected?' I continue, glad that we are at least engaging in conversation. "To what, old boy?"

"To whatever else that was layering Brick Lane. Certainly not the victim's neck though, dear Doctor."

"The blood and viscera? Outside of a slaughterhouse, I have never seen such a mess."

"Vile indeed," Holmes agrees. "Are you so sure though, Watson?"

"Sure? Of what?"

He turns quickly, bolting from the window like he's been bitten by an adder.

"Holmes?" I ask. "What the devil-"

"Come, Watson!" he shouts, throwing open the door. "And bring your gun, if you please."

"What?"

I am pulling on my socks and shoes, still damp from the rain, as I hear him call from the corridor.

"Are you so sure it is a man at all?" Holmes' voice echoes.

Feeling that now familiar chill up my spine, I take my gun from the drawer in my office, grab my coat and give chase.

I race into the street outside our lodgings, very nearly colliding with a clutch of lingering street urchins. Bullying them with harsh words, even though I know I am at fault, I find Holmes standing by the corner of Baker Street looking out into the void.

Night is encroaching, brought on faster by the rain, and my colleague is a tall and gaunt silhouette.

He seizes an urchin as they scurry past, teasing the wretch's ear and having a quiet word. By the time I catch up to them, Holmes has released the boy and is proffering a pocket watch I recognise.

"Yours, I believe, Watson," he says, without looking at me.

I take it, staring vengefully after the little h.e.l.lion that's just disappeared into the darkness, and am about to thank my colleague when he exclaims, "There!" and hares off into the night.

"Holmes?"

I follow, keeping a hand near the pocket where I've put my gun.

"This way, Watson," I hear him cry, his form becoming ever more spectral and seemingly incorporeal the farther ahead he gets.

"Slow down, Holmes," I urge, but he is a hound with the scent of the fox and has no intention of losing the hunt. It is all I can do to keep him vaguely in my line of sight.

We are racing through the London streets and despite my best efforts I lose track of exactly where, my bearings foiled by the night's darkness.

After a long and enervating sprint, Holmes takes a sharp turn and I lose him, just for a few moments. I barrel around the end of a street corner and find it empty.

"Holmes!" I call, worried that I might have lost his trail or my colleague had fallen foul to some urban predator. The area is industrial, as is much of London beyond the tenement squalor, and I hear the action of distant machineries going through their circadian motions.

"Shhh..." I hear from behind me, and turn to see Holmes crouched down in the lee of a doorway. More precisely, I realise, we are in a warehouse district and enclosed on either side by buildings devoted to public works. In the sudden stillness, above the frenzied beating of my own heart, I discern the mechanical grind of the pumping works that services all of London's sewers and drains. The stink of that dank place is strong here too and I wonder suddenly what we have unwittingly walked into.

Holmes is pointing. "At the end of the alley," he says.

I follow his extended finger and see only darkness at first.

My breathing is rapid, my heart rate elevated, and not from the impromptu burst of exercise.

"From Brick Lane," Holmes adds in a rasp, "we were followed."

I can still see only darkness, and then, with all the slow resolution of an eclipse, a shadow detaches itself from another and, at the back of the alley, I see what appears to be a man.

Certainly it is human in shape, two arms, two legs, a head, but the silhouette it creates is ma.s.sive. I gauge it then as over seven feet tall, but my estimate is later proven false.

"Reveal yourself!" I declare with greater courage than I feel.

He has an odour, this giant, one of ammonia and embalming fluid, of naphtha and menthol. There is something else too, a hint only. Decomposition.

Holmes hisses in my ear, and it takes all of my resolve not to cry out in panic, "Did you bring your gun, Doctor?"

Silence has fallen upon the narrow cordon in which we have found ourselves, the actions of the pistons and the wheels of the waterworks unable to lift the strange quietude that has descended. I am not ashamed to admit my hand is trembling as I reach for the gun.

The giant man advances a step, and I am suddenly, disquietingly reminded of how empty the streets now are, of how isolated we must be in a city teeming with souls. None have ventured here, braving the shadows and the rain-soaked night. Save us.

A word manifests in my brain as I look upon this hulking brute and brandish my pistol.

Monster.

"Halt," I warn the man. "Do not come any closer or I will shoot. I am a trained military marksman, I warn you. I shall not miss."

Holmes steps out from the alcove. I see he too has brought a gun.

The giant comes closer and a baleful moan pa.s.ses his lips, like air escaping a leather balloon through its st.i.tches. I hear something else too, the sc.r.a.pe of metal against stone, and I realise that the giant walks with a limp.

"Halt, I say!" shouting to convey my vehemence and commitment. "Step no closer."

Then I fire, a single shot aimed at the heart.

Holmes fires a fraction before me, targeting the head.

There is a brief flash of light from the muzzles of our guns, in which I see the suggestion of something grotesque and misshapen, pallid flesh and a snarl of blackened teeth. The after-flare blinds me, but I hear Holmes reloading for a second shot. I do too, but by the time I have the bullet primed the giant figure has gone.

"Where is he?" I ask, searching the shadows, half-expecting one of them to move.

"John..." says Holmes, pistol held forward in his outstretched hand, advancing into the darkness.

He rarely uses my Christian name. It is usually something he holds in reserve for when he wants to express sentiment but finds he does not possess the emotional faculty to do so. I think now he means to convey the seriousness of the danger we are in and his own exasperation at being confounded by what we had just witnessed.

"I have you covered, old boy," I reply. "Proceed with caution, Sherlock."

He does, the veneer of the reckless showman he often adopts dissolving like all the light of the gas lamps behind us. We are surrounded, he and I, by the shadows and everything they might harbour.

Lowering the pistol, he quickens his pace, just as I settle into a two-handed firing stance. My hands are steady as I am suddenly cast back to Afghanistan and the ranges where I learned my craft as a soldier before being deployed more usefully as a medic. At this moment, I would prefer those war-torn fields to this endless and unknown dark.

Holmes ducks down and I lose him to the shadows.

"Sherlock?" I call.

A few seconds lapse without answer. They stretch into minutes.

"I'm all right, John," he says at last, before adding, "Join me, if you please. I believe I have found how our ugly duckling flew the coop."

I venture into the alley, following my colleague's footsteps, and note as I get closer that there is a dead end, a blank wall to which the grotesque giant could not simply have dematerialised.

Holmes is crouching by a barred vent through which the noisome gases of the sewer emanate. As I join him, I try not to gag.

"Holmes, how can you not retch at the smell of it?"

He doesn't say, but instead directs my attention to a faint sc.r.a.ping next to the sewer grate.

"Light?" he asks.

"I beg your pardon, Holmes?"

"Light, illumination, a match, Watson," he expounds with some exasperation. "Do you have a match upon your person, Doctor?"

I do, and produce the book from my pocket, which Holmes s.n.a.t.c.hes in short order. Striking one before I can protest, the scratches next to the grate are revealed in greater detail, as is the size and heft of the iron barrier blocking our own ingress in the dank darkness of London's effluent underworld.

"It would take three men to lift that," I observe, not bothering to hide my shock that our giant seemingly managed the feat alone.

"A pity then," says Holmes, "that we are only two."

After a tense pause as we stare into the mouth of the grate, I say, "I hit him, Holmes. A heart shot, I have no doubt."

Holmes looks at me sidelong. "No doubt, Doctor? In this gloom, your body fighting to overwhelm its very natural urge to flee? Can you be that precise?"

I nod. "In the heart, Holmes. I am sure."

He regards me for a moment then nods himself. "Very well then."

"And you?" I ask.

"The head. Left temple. Certain to kill or severely debilitate in the unlikely probability the bullet ricocheted off the skull and away from the brain."

"Then why-" I begin, before Holmes interrupts.

"Is our grotesque not dead? That is an excellent question."

His gaze has returned to the grate, and I see the yearning in his eyes to know the solution to this puzzle before us. Then the match fades and we are enveloped by shadow again.

"Would you venture down there?" I ask.

There is a moment of silence from Holmes when I a.s.sume he is contemplating that very course, before he stands up straight and dusts off his hands.

"No, I think that would be unwise. Our grotesque is not far away, I believe. He is waiting for us," he says louder, presumably for the benefit of the giant.

We leave the alleyway and the sounds of the waterworks behind us. It is a long way back to Baker Street, made longer by my imaginings. I am not ashamed to admit the experience shook me to my core. Not since the moors and our encounter with the beast that preyed there have I been so afraid.