It was half-past five before Holmes returned. He was bright,eager, and in excellent spirits, a mood which in his case alter-nated with fits of the blackest depression.

"There is no great mystery in this matter," he said, taking thecup of tea which I had poured out for him; "the facts appear toadmit of only one explanation."

"What! you have solved it already?"

"Well, that would be too much to say. I have discovered asuggestive fact, that is all. It is, however, very suggestive. Thedetails are still to be added. I have just found, on consulting theback files of the Times, that Major Sholto, of Upper Norwood,late of the Thirty-fourth Bombay Infantry, died upon the twenty-eighth of April, 1882."

"I may be very obtuse, Holmes, but I fail to see what thissuggests."

"No? You surprise me. Look at it in this way, then. CaptainMorstan disappears. The only person in London whom he couldhave visited is Major Sholto. Major Sholto denies having heardthat he was in London. Four years later Sholto dies. Within aweek of his death Captain Morstan's daughter receives a valuablepresent, which is repeated from year to year and now culminatesin a letter which describes her as a wronged woman. Whatwrong can it refer to except this deprivation of her father? Andwhy should the presents begin immediately after Sholto's deathunless it is that Sholto's heir knows something of the mysteryand desires to make compensation? Have you any alternativetheory which will meet the facts?"

"But what a strange compensation! And how strangely made!Why, too, should he write a letter now, rather than six yearsago? Again, the letter speaks of giving her justice. What justicecan she have? It is too much to suppose that her father is stillalive. There is no other injustice in her case that you know of."

"There are difficulties; there are certainly difficulties," saidSherlock Holmes pensively; "but our expedition of to-night willsolve them all. Ah, here is a four-wheeler, and Miss Morstan isinside. Are you all ready? Then we had better go down, for it isa little past the hour."

I picked up my hat and my heaviest stick, but I observed thatHolmes took his revolver from his drawer and slipped it into hispocket. It was clear that he thought that our night's work mightbe a serious one.

Miss Morstan was muffled in a dark cloak, and her sensitiveface was composed but pale. She must have been more thanwoman if she did not feel some uneasiness at the strange enter-prise upon which we were embarking, yet her self-control wasperfect, and she readily answered the few additional questionswhich Sherlock Holmes put to her.

"Major Sholto was a very particular friend of Papa's," shesaid. "His letters were full of allusions to the major. He andPapa were in command of the troops at the Andaman Islands, sothey were thrown a great deal together. By the way, a curiouspaper was found in Papa's desk which no one could understand.I don't suppose that it is of the slightest importance, but Ithought you might care to see it, so I brought it with me. It ishere."

Holmes unfolded the paper carefully and smoothed it out uponhis knee. He then very methodically examined it all over with hisdouble lens.

"It is paper of native Indian manufacture," he remarked. "Ithas at some time been pinned to a board. The diagram upon itappears to be a plan of part of a large building with numeroushalls, corridors, and passages. At one point is a small cross donein red ink, and above it is '3.37 from left,' in faded pencil-writing. In the left-hand corner is a curious hieroglyphic like fourcrosses in a line with their arms touching. Beside it is written, invery rough and coarse characters, 'The sign of the four -- JonathanSmall, Mahomet Singh, Abdullah Khan, Dost Akbar.' No, Iconfess that I do not see how this bears upon the matter. Yet it isevidently a document of importance. It has been kept carefully ina pocketbook, for the one side is as clean as the other."

"It was in his pocketbook that we found it."

"Preserve it carefully, then, Miss Morstan, for it may prove tobe of use to us. I begin to suspect that this matter may turn out tobe much deeper and more subtle than I at first supposed. I mustreconsider my ideas."

He leaned back in the cab, and I could see by his drawn browand his vacant eye that he was thinking intently. Miss Morstanand I chatted in an undertone about our present expedition and itspossible outcome, but our companion maintained his impenetra-ble reserve until the end of our journey.

It was a September evening and not yet seven o'clock, but theday had been a dreary one, and a dense drizzly fog lay low uponthe great city. Mud-coloured clouds drooped sadly over themuddy streets. Down the Strand the lamps were but misty splotchesof diffused light which threw a feeble circular glimmer upon theslimy pavement. The yellow glare from the shop-windows streamedout into the steamy, vaporous air and threw a murky, shiftingradiance across the crowded thoroughfare. There was, to mymind, something eerie and ghostlike in the endless procession offaces which flitted across these narrow bars of light -- sad facesand glad, haggard and merry. Like all humankind, they flittedfrom the gloom into the light and so back into the gloom oncemore. I am not subject to impressions, but the dull, heavyevening, with the strange business upon which we were engaged,combined to make me nervous and depressed. I could see fromMiss Morstan's manner that she was suffering from the samefeeling. Holmes alone could rise superior to petty influences. Heheld his open notebook upon his knee, and from time to time hejotted down figures and memoranda in the light of his pocket-lantern.

At the Lyceum Theatre the crowds were already thick at theside-entrances. In front a continuous stream of hansoms andfour-wheelers were rattling up, discharging their cargoes of shirt-fronted men and beshawled, bediamonded women. We had hardlyreached the third pillar, which was our rendezvous, before asmall, dark, brisk man in the dress of a coachman accosted us.

"Are you the parties who come with Miss Morstan?" heasked.

"I am Miss Morstan, and these two gentlemen are my friends,"said she.

He bent a pair of wonderfully penetrating and questioning eyesupon us.

"You will excuse me, miss," he said with a certain doggedmanner, "but I was to ask you to give me your word that neitherof your companions is a police-officer."

"I give you my word on that," she answered.

He gave a shrill whistle, on which a street Arab led across afour-wheeler and opened the door. The man who had addressedus mounted to the box, while we took our places inside. We hadhardly done so before the driver whipped up his horse, and weplunged away at a furious pace through the foggy streets.

The situation was a curious one. We were driving to anunknown place, on an unknown errand. Yet our invitation waseither a complete hoax -- which was an inconceivable hypothesis --or else we had good reason to think that important issues mighthang upon our journey. Miss Morstan's demeanour was as reso-lute and collected as ever. I endeavoured to cheer and amuse herby reminiscences of my adventures in Afghanistan; but, to tellthe truth, I was myself so excited at our situation and so curiousas to our destination that my stories were slightly involved. Tothis day she declares that I told her one moving anecdote as tohow a musket looked into my tent at the dead of night, and howI fired a double-barrelled tiger cub at it. At first I had some ideaas to the direction in which we were driving; but soon, what withour pace, the fog, and my own limited knowledge of London, Ilost my bearings and knew nothing save that we seemed to begoing a very long way. Sherlock Holmes was never at fault,however, and he muttered the names as the cab rattled throughsquares and in and out by tortuous by-streets.

"Rochester Row," said he. "Now Vincent Square. Now wecome out on the Vauxhall Bridge Road. We are making for theSurrey side apparently. Yes, I thought so. Now we are on thebridge. You can catch glimpses of the river."

We did indeed get a fleeting view of a stretch of the Thames,with the lamps shining upon the broad, silent water; but our cabdashed on and was soon involved in a labyrinth of streets uponthe other side.

"Wordsworth Road," said my companion. "Priory Road.Lark Hall Lane. Stockwell Place. Robert Street. Cold HarbourLane. Our quest does not appear to take us to very fashionableregions."

We had indeed reached a questionable and forbidding neigh-bourhood. Long lines of dull brick houses were only relieved bythe coarse glare and tawdry brilliancy of public-houses at thecorner. Then came rows of two-storied villas, each with a front-ing of miniature garden, and then again interminable lines ofnew, staring brick buildings -- the monster tentacles which thegiant city was throwing out into the country. At last the cab drewup at the third house in a new terrace. None of the other houseswere inhabited, and that at which we stopped was as dark as itsneighbours, save for a single glimmer in the kitchen-window. Onour knocking, however, the door was instantly thrown open by aHindoo servant, clad in a yellow turban, white loose-fittingclothes, and a yellow sash. There was something strangely in-congruous in this Oriental figure framed in the commonplacedoorway of a third-rate suburban dwelling-house.

"The sahib awaits you," said he, and even as he spoke, therecame a high, piping voice from some inner room.

"Show them in to-me, khitmutgar," it said. "Show themstraight in to me."