as the police boat left limehouse pier, a clammy south-easterly breeze blowing up-stream lifted the fog in clearly defined layers, an effect very singular to behold. at one moment a great arc-lamp burning above the lavender pond of the surrey commercial dock shot out a yellowish light across the thames. then, as suddenly as it had come, the light vanished again as a stratum of mist floated before it.

the creaking of the oars sounded muffled and ghostly, and none of the men in the boat seemed to be inclined to converse. heading across stream they made for the unseen promontory of the isle of dogs. navigation was suspended, and they reached midstream without seeing a ship's light. then came the damp wind again to lift the fog, and ahead of them they discerned one of the general steam navigation company's boats awaiting an opportunity to make her dock at the head of deptford creek. the clamor of an ironworks on the millwall shore burst loudly upon their ears, and away astern the lights of the surrey dock shone out once more. hugging the bank they pursued a southerly course, and from limehouse reach crept down to greenwich reach.

fog closed in upon them, a curtain obscuring both light and sound. when the breeze came again it had gathered force, and it drove the mist before it in wreathing banks, and brought to their ears a dull lowing and to their nostrils a farmyard odor from the cattle pens. ghostly flames, leaping and falling, leaping and falling, showed where a gasworks lay on the greenwich bank ahead.

eastward swept the river now, and fresher blew the breeze. as they rounded the blunt point of the “isle” the fog banks went swirling past them astern, and the lights on either shore showed clearly ahead. a ship's siren began to roar somewhere behind them. the steamer which they had passed was about to pursue her course.

closer in-shore drew the boat, passing a series of wharves, and beyond these a tract of waste, desolate bank very gloomy in the half light and apparently boasting no habitation of man. the activities of the greenwich bank seemed remote, and the desolation of the isle of dogs very near, touching them intimately with its peculiar gloom.

a light sprang into view some little distance inland, notable because it shone lonely in an expanse of utter blackness. kerry broke the long silence.

“dougal's,” he said. “put us ashore here.”

the police boat was pulled in under a rickety wooden structure, beneath which the thames water whispered eerily; and kerry and seton disembarked, mounting a short flight of slimy wooden steps and crossing a roughly planked place on to a shingly slope. climbing this, they were on damp waste ground, pathless and uninviting.

“dougal's is being watched,” said kerry. “i think i told you?”

“yes,” replied seton. “but i have formed the opinion that the dope gang is too clever for the ordinary type of man. sin sin wa is an instance of what i mean. neither you nor i doubt that he is a receiver of drugs—perhaps the receiver; but where is our case? the only real link connecting him with the west-end habitue is his wife. and she has conveniently deserted him! we cannot possibly prove that she hasn't while he chooses to maintain that she has.”

“h'm,” grunted kerry, abruptly changing the subject. “i hope i'm not recognized here.”

“have you visited the place before?”

“some years ago. unless there are any old hands on view tonight, i don't think i shall be spotted.”

he wore a heavy and threadbare overcoat, which was several sizes too large for him, a muffler, and a weed cap—the outfit supplied by seton pasha; and he had a very vivid and unpleasant recollection of his appearance as viewed in his little pocket-mirror before leaving seton's room. as they proceeded across the muddy wilderness towards the light which marked the site of dougal's, they presented a picture of a sufficiently villainous pair.

the ground was irregular, and the path wound sinuously about mounds of rubbish; so that often the guiding light was lost, and they stumbled blindly among nondescript litter, which apparently represented the accumulation of centuries. but finally they turned a corner formed by a stack of rusty scrap iron, and found a long, low building before them. from a ground-floor window light streamed out upon the fragments of rubbish strewing the ground, from amid which sickly weeds uprose as if in defiance of nature's laws. seton paused, and:

“what is dougal's exactly?” he asked; “a public house?”

“no,” rapped kerry. “it's a coffee-shop used by the dockers. you'll see when we get inside. the place never closes so far as i know, and if we made 'em close there would be a dock strike.”

he crossed and pushed open the swing door. as seton entered at his heels, a babel of coarse voices struck upon his ears and he found himself in a superheated atmosphere suggestive of shag, stale spirits, and imperfectly washed humanity.

dougal's proved to be a kind of hut of wood and corrugated iron, not unlike an army canteen. there were two counters, one at either end, and two large american stoves. oil lamps hung from the beams, and the furniture was made up of trestle tables, rough wooden chairs, and empty barrels. coarse, thick curtains covered all the windows but one. the counter further from the entrance was laden with articles of food, such as pies, tins of bully-beef, and “saveloys,” while the other was devoted to liquid refreshment in the form of ginger-beer and cider (or so the casks were conspicuously labelled), tea, coffee, and cocoa.

the place was uncomfortably crowded; the patrons congregating more especially around the two stoves. there were men who looked like dock laborers, seamen, and riverside loafers; lascars, chinese, arabs, and dagoes; and at the “solid” counter there presided a red-armed, brawny woman, fierce of mien and ready of tongue, while a huge irishman, possessing a broken nose and deficient teeth, ruled the “liquid” department with a rod of iron and a flow of language which shocked even kerry. this formidable ruffian, a retired warrior of the ring, was dougal, said to be the strongest man from tower hill to the river lea.

as they entered, several of the patrons glanced at them curiously, but no one seemed to be particularly interested. kerry wore his cap pulled well down over his fierce eyes, and had the collar of his topcoat turned up.

he looked about him, as if expecting to recognize someone; and as they made their way to dougal's counter, a big fellow dressed in the manner of a dock laborer stepped up to the chief inspector and clapped him on the shoulder.

“have one with me, mike,” he said, winking. “the coffee's good.”

kerry bent towards him swiftly, and:

“anybody here, jervis?” he whispered.

“george martin is at the bar. i've had the tip that he 'traffics.' you'll remember he figured in my last report, sir.”

kerry nodded, and the trio elbowed their way to the counter. the pseudo-dock hand was a detective attached to leman street, and one who knew the night birds of east end london as few men outside their own circles knew them.

“three coffees, pat,” he cried, leaning across the shoulder of a heavy, red-headed fellow who lolled against the counter. “and two lumps of sugar in each.”

“to hell wid yer sugar!” roared dougal, grasping three cups deftly in one hairy hand and filling them from a steaming urn. “there's no more sugar tonight.”

“not any brown sugar?” asked the customer.

“yez can have one tayspoon of brown, and no more tonight,” cried dougal.

he stooped rapidly below the counter, then pushed the three cups of coffee towards the detective. the latter tossed a shilling down, at which dougal glared ferociously.

“'twas wid sugar ye said!” he roared.

a second shilling followed. dougal swept both coins into a drawer and turned to another customer, who was also clamoring for coffee. securing their cups with difficulty, for the red-headed man surlily refused to budge, they retired to a comparatively quiet spot, and seton tasted the hot beverage.

“h'm,” he said. “rum! good rum, too!”

“it's a nice position for me,” snapped kerry. “i don't think i would remind you that there's a police station actually on this blessed island. if there was a dive like dougal's anywhere west it would be raided as a matter of course. but to shut dougal's would be to raise hell. there are two laws in england, sir; one for piccadilly and the other for the isle of dogs!” he sipped his coffee with appreciation. jervis looked about him cautiously, and:

“that's george—the red-headed hooligan against the counter,” he said. “he's been liquoring up pretty freely, and i shouldn't be surprised to find that he's got a job on tonight. he has a skiff beached below here, and i think he's waiting for the tide.”

“good!” rapped kerry. “where can we find a boat?”

“well,” jervis smiled. “there are several lying there if you didn't come in an r.p. boat.”

“we did. but i'll dismiss it. we want a small boat.”

“very good, sir. we shall have to pinch one!”

“that doesn't matter,” declared kerry glancing at seton with a sudden twinkle discernible in his steely eyes. “what do you say, sir?”

“i agree with you entirely,” replied seton quietly. “we must find a boat, and lie off somewhere to watch for george. he should be worth following.”

“we'll be moving, then,” said the leman street detective. “it will be high tide in an hour.”

they finished their coffee as quickly as possible; the stuff was not far below boiling-point. then jervis returned the cups to the counter. “good night, pat!” he cried, and rejoined seton and kerry.

as they came out into the desolation of the scrap heaps, the last traces of fog had disappeared and a steady breeze came up the river, fresh and salty from the nore. jervis led them in a north-easterly direction, threading a way through pyramids of rubbish, until with the wind in their teeth they came out upon the river bank at a point where the shore shelved steeply downwards. a number of boats lay on the shingle.

“we're pretty well opposite greenwich marshes,” said jervis. “you can just see one of the big gasometers. the end boat is george's.”

“have you searched it?” rapped kerry, placing a fresh piece of chewing-gum between his teeth.

“i have, sir. oh, he's too wise for that!”

“i propose,” said seton briskly, “that we borrow one of the other boats and pull down stream to where that short pier juts out. we can hide behind it and watch for our man. i take it he'll be bound up-stream, and the tide will help us to follow him quietly.”

“right,” said kerry. “we'll take the small dinghy. it's big enough.”

he turned to jervis.

“nip across to the wooden stairs,” he directed, “and tell inspector white to stand by, but to keep out of sight. if we've started before you return, go back and join him.”

“very good, sir.”

jervis turned and disappeared into the mazes of rubbish, as seton and kerry grasped the boat and ran it down into the rising tide. kerry boarding, seton thrust it out into the river and climbed in over the stern.

“phew! the current drags like a tow-boat!” said kerry.

they were being drawn rapidly up-stream. but as kerry seized the oars and began to pull steadily, this progress was checked. he could make little actual headway, however.

“the tide races round this bend like fury,” he said. “bear on the oars, sir.”

seton thereupon came to kerry's assistance, and gradually the dinghy crept upon its course, until, below the little pier, they found a sheltered spot, where it was possible to run in and lie hidden. as they won this haven:

“quiet!” said seton. “don't move the oars. look! we were only just in time!”

immediately above them, where the boats were beached, a man was coming down the slope, carrying a hurricane lantern. as kerry and seton watched, the man raised the lantern and swung it to and fro.

“watch!” whispered seton. “he's signalling to the greenwich bank!”

kerry's teeth snapped savagely together, and he chewed but made no reply, until:

“there it is!” he said rapidly. “on the marshes!”

a speck of light in the darkness it showed, a distant moving lantern on the curtain of the night. although few would have credited kerry with the virtue, he was a man of cultured imagination, and it seemed to him, as it seemed to seton pasha, that the dim light symbolized the life of the missing woman, of the woman who hovered between the gay world from which tragically she had vanished and some chinese hell upon whose brink she hovered. neither of the watchers was thinking of the crime and the criminal, of sir lucien pyne or kazmah, but of mrs. monte irvin, mysterious victim of a mysterious tragedy. “oh, dan! ye must find her! ye must find her! puir weak hairt—dinna ye ken how she is suffering!” clairvoyantly, to kerry's ears was borne an echo of his wife's words.

“the traffic!” he whispered. “if we lose george martin tonight we deserve to lose the case!”

“i agree, chief inspector,” said seton quietly.

the grating sound made by a boat thrust out from a shingle beach came to their ears above the whispering of the tide. a ghostly figure in the dim light, george martin clambered into his craft and took to the oars.

“if he's for the greenwich bank,” said seton grimly, “he has a stiff task.”

but for the greenwich bank the boat was headed; and pulling mightily against the current, the man struck out into mid-stream. they watched him for some time, silently, noting how he fought against the tide, sturdily heading for the point at which the signal had shown. then:

“what do you suggest?” asked seton. “he may follow the surrey bank up-stream.”

“i suggest,” said kerry, “that we drift. once in limehouse reach we'll hear him. there are no pleasure parties punting about that stretch.”

“let us pull out, then. i propose that we wait for him at some convenient point between the west india dock and limehouse basin.”

“good,” rapped kerry, thrusting the boat out into the fierce current. “you may have spent a long time in the east, sir, but you're fairly wise on the geography of the lower thames.”

gripped in the strongly running tide they were borne smoothly up-stream, using the oars merely for the purpose of steering. the gloomy mystery of the london river claimed them and imposed silence upon them, until familiar landmarks told of the northern bend of the thames, and the light above the lavender pond shone out upon the unctuously moving water.

each pulling a scull they headed in for the left bank.

“there's a wharf ahead,” said seton, looking back over his shoulder. “if we put in beside it we can wait there unobserved.”

“good enough,” said kerry.

they bent to the oars, stealing stroke by stroke out of the grip of the tide, and presently came to a tiny pool above the wharf structure, where it was possible to lie undisturbed by the eager current.

those limitations which are common to all humanity and that guile which is peculiar to the chinese veiled the fact from their ken that the deserted wharf, in whose shelter they lay, was at once the roof and the gateway of sin sin wa's receiving office!

as the boat drew in to the bank, a chinese boy who was standing on the wharf retired into the shadows. from a spot visible down-stream but invisible to the men in the boat, he signalled constantly with a hurricane lantern.

three men from new scotland yard were watching the house of sin sin wa, and sin sin wa had given no sign of animation since, some hours earlier, he had extinguished his bedroom light. yet george, drifting noiselessly up-stream, received a signal to the effect “police” while seton pasha and chief inspector kerry lay below the biggest dope cache in london. seton sometimes swore under his breath. kerry chewed incessantly. but george never came.

at that eerie hour of the night when all things living, from the lowest to the highest, nor excepting mother earth herself, grow chilled, when all nature's perishable handiwork feels the touch of death—a wild, sudden cry rang out, a wailing, sorrowful cry, that seemed to come from nowhere, from everywhere, from the bank, from the stream; that rose and fell and died sobbing into the hushed whisper of the tide.

seton's hand fastened like a vise on to kerry's shoulder, and:

“merciful god!” he whispered; “what was it? who was it?”

“if it wasn't a spirit it was a woman,” replied kerry hoarsely; “and a woman very near to her end.”

“kerry!”—seton pasha had dropped all formality—“kerry—if it calls for all the men that scotland yard can muster, we must search every building, down to the smallest rathole in the floor, on this bank—and do it by dawn!”

“we'll do it,” rapped kerry.