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 bee............