A thin grey mist lay upon the waters, giving the impression of a silvery veil of gauze stretched from sea to sky. The evening was calm, with not a breath of wind stirring, and the sea was ruffled by long, undulating furrows that pursued their way across the surface like great ripples, with never a "cat's paw" nor a speck of foam to break the monotony of their green-grey hue.

Looking strangely impalpable and ghostlike by reason of the mist, the destroyer Knat slipped swiftly through the water, heaving gently to the ground-swell. Upon the bridge Lieutenant-Commander Lawless stood smoking a pipe, and near him Sub-Lieutenant Trent reclined against the searchlight, likewise absorbing tobacco smoke and ozone. No other vessel was in sight and the only sound to be heard was the soft whirr of the turbines.

"This is what I call balmy and peaceful," remarked Lawless, taking the pipe from his mouth and knocking it against the handrail. "One could almost sing 'A Life on the Ocean Wave.'"

"Huh!" grunted Trent; "then it would be balmy without being peaceful."

As Lawless made no reply, he looked up to see the Lieutenant staring hard through the mist at a vague, shapeless something which might have been a ship, or a cliff, viewed through the murky atmosphere.

"Something ahead of us on the starboard bow," he said.

Both officers riveted their gaze upon the nebulous object which, as the destroyer overhauled it, assumed the shape and appearance of a large steamer, while their ears caught the steady throb of engines.

"I'll give her a hail," said Lawless, picking up the megaphone.

But before he had time to raise it to his mouth the fog was split by a yellow streak of fire and a shell came whizzing over the Knat's bows.

"By the Lord, an enemy ship!" ejaculated the Lieutenant, and passed the word to open fire with the machine guns. The quick-firer just below the bridge led off, but before the other guns had a chance to follow suit a heavy bank of fog rolled up and obliterated the steamer as completely as though a curtain had been lowered. Although invisible, the vessel's engines could still be heard and, guided by the sound, the Knat was kept on her trail, Lawless waiting only for the fog to lift in order to open fire again. While he was still expecting this to happen there came the notes of a bugle and at the sound the Lieutenant nearly tumbled down the bridge ladder in astonishment. For it was the dinner call as given on British ships:

"What the dickens does it mean?" he murmured, and then, raising his voice, hailed the mysterious steamer.

"Ahoy there, ahoy! Where away?" came the answer.

"On your port quarter."

"What ship is that?"

"British destroyer, Knat."

The fog lifted again, and this time Lawless could see the decks thronged with anxious passengers and the captain leaning over the port bridge-rail.

"What ship are you?" he shouted.

"The Cotswold, for Hull. Just sighted an enemy submarine and opened fire on her," came the answer.

"A submarine! How long ago?"

"About ten minutes. She was using her machine-gun."

"Why don't you provide your look-outs with spectacles?" answered Lawless wrathfully. "It was me you sighted, not a submarine!"

"I saw her periscope," answered the skipper of the Cotswold.

"Saw your grandmother! You opened fire on me and I replied."

"Then it was your business to hail me. Pity you haven't something better to do than take pot shots at passenger boats," answered the merchant skipper with some heat.

The latter was obviously in the wrong, but, as a matter of fact, during his voyage across the Atlantic he had been chased by two enemy submarines and only by skilful seamanship and unceasing vigilance had succeeded in eluding them and saving his ship. He was, therefore, a trifle "nervy" and apt to suspect every indistinguishable floating object he met of being a submarine. Possibly, seen dimly through the fog, the Knat looked something like a submarine awash and the captain of the Cotswold had been justified in opening fire on her. Lawless, however, was ignorant of this, and the skipper's last taunt made him almost dance with rage. Fortunately, perhaps, another fog bank rolled up at this moment and the two vessels were again hidden from each other.

For some moments Lawless growled to himself things which, had the captain of the Cotswold heard them, might have produced a resumption of hostilities. Suddenly he gave vent to an exclamation:

"I've got it!"

"Got what?" inquired Trent.

"An idea."

"Extraordinary phenomenon; I'll have to make a note of it in the log. 'Seven p.m. Commanding Officer seized——'"

"Don't try and be funny, it's too pathetic. What I'm going to do is to give that skipper the biggest shaking up he's ever had. If I don't get even with him you can call me Von Tirpitz and I'll turn the other cheek."

"It sounds exciting."

"You'll see," answered Lawless, and, leaving Trent in charge of the bridge, he disappeared down the companion ladder.

A few minutes later a sound of hammering reached the Sub-Lieutenant's ears, and this went on, at intervals, for nearly a quarter of an hour. Presently Lawless emerged upon the after-deck, followed by two seamen carrying a barrel with what looked like a piece of stove-pipe protruding from it.

"There," said Lawless, mounting the bridge again. "Isn't it a daisy?"

"What is it—a patent incubator?" inquired Trent.

"Pah! You've no imagination. That, my son, is an idea."

"H'm! I always thought your ideas were pretty heavy, but——"

"Shut up or I'll report you for insubordination."

"Sorry, but I don't quite follow the drift of this ponderous idea of yours."

"That's because yours is a stodgy, matter-of-fact, unromantic mind. But listen and I'll expound in words suitable to your infantine understanding. In the first place, I must tell you that one end of that barrel is weighted in such a manner that, when submerged in a suitable fluid, such as sea-water, it will float just below the surface. Secondly," continued Lawless, in the manner of one giving a lecture, "I would call your attention to a cylindrical object which, viewed at close range, somewhat resembles a drain-pipe. Nevertheless, my child, it is not a drain-pipe, but an invention of mine own constructed by the worthy artificer, yclept Bates. Lastly, a thin line of about six fathoms length, to the end of which is suspended a goodly lump of lead, is attached to the side of the said barrel."

Lawless stopped and waited for the applause.

"A very pretty conjuring trick," remarked Trent, as one humouring an amiable lunatic. "And what do you do now? Make it disappear up your sleeve or change it into a live rabbit?"

"Oh, you blithering ass!" exclaimed the Lieutenant impatiently. "Can't you see? This is the means I've devised for revenging myself on that wretched skipper."

"You're going to fill it with dynamite and explode it under his stern?"

"No, my child, I'm not. Instead, I'm going to fix that line to the stanchions against his rudder-post so that the steamer will tow this barrel, which, being weighted, will be submerged and show only the pipe in a vertical position above the surface. Furthermore, the worthy Bates having fashioned the top thereof in the likeness of a periscope, the victim will think he's being chased by an enemy submarine and have divers fits and spasms in consequence. Do you grasp the idea now?"

"It's pretty feeble, but I think I follow you," answered Trent. "Only you seem to have forgotten one thing, which is that as soon as the fog lifts and the skipper spots your barrel he'll pot it with his quick-firer. Then we shall read a hair-raising account of how the captain of the Cotswold sank a U boat which had been following her all night."

"Not a bit of it, my son. They won't be able to hit that barrel in a month of Sundays, especially if we get a choppy sea by the morning."

Trent shrugged his shoulders, but made no further comment.

"And now," went on Lawless cheerfully, "it's time the plot thickened, so we'll proceed to drop the bean in the soup. Stand by the telegraph, for if we run our nose against the other fellow's counter the joke'll be on us."

He leant over the bridge-rail and peered through the fog for the steamer, but, though he could hear the latter's engines, the vessel herself was invisible. The manoeuvre he proposed carrying out was, to put it mildly, risky, and no one but the feckless Lieutenant would have contemplated such a thing, much less have attempted to put it into execution. But no fear of possible consequences ruffled his serenity as, little by little, the Knat cautiously overhauled the Cotswold, the noise of whose machinery completely drowned the hum of the destroyer's turbines.

Some ten minutes elapsed, and then Lawless was able to make out the vessel's stern towering, dim and shadowy, above him. Then, taking the wheel from the hands of the quartermaster, he brought the Knat's bows right under the steamer's counter.

"Let her go," he said in a hoarse whisper.

The bos'n, who was balancing himself on the companion-ladder, sprang to the deck and, picking up the line attached to the barrel, ran with it on to the fo'c'sle head. Leaning as far over as he could he pitched the lump of lead, to which the other end of the line was fastened, against the Cotswold's stern-post in such a manner that it would fall over one of the iron supports extending from beneath the counter to the rudder-post. There was, of course, the danger of its being caught in the propellers, but he had to risk that. As it happened, the cast was successful, whereupon the bos'n called softly to a sailor, who at once flung the barrel into the sea, together with the slack line.

"All clear, sir," the bos'n reported to Lawless.

The latter rang down "half-speed astern," the Knat backed away into the fog, and the steamer was blotted out.

"There," murmured the Lieutenant, with a sigh of satisfaction, "when the skipper spots that in his wake he'll have about fifty fits right away. Now we'd better try and get back on our beat."

The Knat was supposed to be searching a certain prescribed area for an enemy mine-sower which had been active for several days past in this particular portion of the North Sea. Lawless, so far, had not had any luck; a fact which made him all the keener to meet with the enemy ship before she succeeded in getting safely back to port.

"I'm going below for a spell," he said to Trent. "Call me if anything happens."

About a couple of hours later, the Lieutenant was awakened by a bridge-messenger, who told him the fog was lifting and that a vessel had just been sighted.

"Looks to be the packet we picked up a little while back, sir," he said.

Lawless proceeded to the bridge and, catching sight of the steamer dimly visible ahead, chuckled softly.

"The fun'll start before long," he remarked to Trent. "Oh, to see the old man's face when the officer of the watch reports a submarine astern!"

"I've calculated that your precious joke's taken us about four miles out of our course," answered the junior officer gloomily.

"You'll meet with an early death, like all good young people, if you're not careful," retorted Lawless. "Virtue has its disadvantages remember."

A mild breeze had sprung up and was dissipating the fog rapidly while churning the water into cat's paws. Presently Trent, who had been watching the steamer through the night glasses, thrust them into the Lieutenant's hands.

"Take a squint at that packet," he said in a tone of suppressed excitement.

Lawless did so, and remained staring at the vessel ahead for such a long time that Trent became impatient.

"Well, what do you make of her?" he asked.

"She's not the Cotswold."

"No; and why is she steaming without lights?"

"We'll soon see," answered Lawless, and rang down full speed ahead.

In a few minutes the destroyer was broadside on to the strange vessel and Lawless shouted a demand to know what ship she was. A pause ensued, and then, by way of an answer, a tongue of flame leapt from the stranger's port side and a shell crashed into the Knat's funnel, just abaft the bridge. In a second the destroyer had swung round so as to present only her bows to the enemy and her machine-guns were hammering away as fast as they could be loaded. The duel lasted nearly ten minutes, the Knat trying to manoeuvre into such a position that she could torpedo her adversary, the latter doing her utmost to frustrate this design. And all this time the two vessels were pounding away at each other with their machine-guns, circling around like two wrestlers before they come to grips. The enemy had the advantage in guns, which were far heavier than those carried by the destroyer, but the latter made up for this in speed and, being so small, proved an extraordinarily difficult target to hit.

At last Lawless saw his chance to launch a torpedo and gave the word. The glistening, fish-like weapon leapt from its tube and, at the same moment, the enemy vessel started to swing round in order to avoid the fast approaching engine of death. But the manoeuvre had been carried out too late; the torpedo struck her just underneath the stern and there was a terrific explosion. The steamer heeled over on her starboard side, her bows lifted above the water, and then, with a roar of escaping steam, she dived stern foremost beneath the surface, and so to the bottom, fifty fathoms deep or more.

The Knat's boats had been launched immediately after the mine-sower was struck, and they at once proceeded to the spot where she had disappeared. But so swift had been the steamer's fate that not more than half a dozen survivors were picked up and, after pulling around for a while, the boats returned to the Knat.

Early in the afternoon of the following day the Knat put into Hull, and Lawless, having handed over his prisoners and written an official report of the engagement, went ashore with Trent.

"By the way," said the latter, as they made their way towards a certain hostelry much favoured by naval and merchant service officers, "did you notice the Cotswold moored just off the landing stage?"

"No, I was below making out my report."

His face expanded into a broad grin.

"Then the chances are ten to one that we meet her skipper before the day's out. And if I don't pull his blessed leg you can strafe me for a Hun."

As it happened they did meet this particular skipper, and in the very hostelry to which they were bound. He was in the smoking-room and, of course, did not recognise Lawless when he and Trent entered because, on the occasion of their exchanging courtesies, it had been too dark and foggy for either of them to identify the other. The Lieutenant, however, knew him at once by his voice, which was of a peculiarly hoarse quality.

"It's a fact," he was saying to a small group of interested auditors, "that infernal U boat was no farther from my stern than I am from that piano yonder. Well, I started steering a zig-zag course, at the same time opening fire on the submarine with my machine-gun. One of the first shots knocked her periscope to smithereens and then——"

He was interrupted by a burst of laughter, and, turning round, the narrator of this thrilling episode beheld a couple of officers almost doubled up with mirth.

"Oh, tell us some more, skipper!" cried Lawless, as soon as he could speak.

"I beg your pardon, sir," said the other, his face scarlet with indignation.

"Then we'll say no more about it," answered the Lieutenant. "But surely you remember me? We met in the fog last night."

"What! Are you the blackguard who fired on me?"

"Well, you started shooting first, remember. But about that submarine yarn of yours, it's such a good one that I really haven't the heart to spoil it; so, if you'll stand drinks round, mum's the word as far as I'm concerned."

"Will you be good enough to tell me what the devil you're driving at?" inquired the skipper, glaring fiercely at Lawless.

"Then you won't accept my offer?"

"Sir, I'll see you in Hades first."

"Very well then, here goes," and Lawless proceeded to recount the trick he had played on the skipper with the aid of a barrel and a tin cylinder. He was interrupted several times by bursts of uproarious mirth from the audience, but the victim himself neither smiled nor uttered a word until the Lieutenant had finished his story.

Then he spoke.

"So you claim that I haven't sunk an enemy submarine at all?" he asked, turning to Lawless.

"I'll wager a month's salary to a pinch of snuff that you never even saw one from the time we parted till you reached port."

"I accept the wager," answered the skipper, to everybody's surprise. "You see," he went on, addressing the company generally, "one reason why I collared that U boat so easily was that something fouled her propeller and she could neither get away nor attack me. This morning, when we put in here, the bos'n found a length of rope with a piece of lead attached, fastened to the vessel's stern. How the deuce it got there we couldn't make out, but now, thanks to this gentleman, we know. What's more, it must have been that rope and the old barrel at the end of it which fouled the German's propeller and did him in. As for proof"—he turned to an elderly gentleman seated in a corner—"there is Captain Barter, who took charge of the prisoners when they were landed, and he can tell you whether my story's true or not."

All eyes were turned inquiringly upon the unobtrusive gentleman with the four gold rings round his sleeves.

"Yes," he said quietly, "it's perfectly true. The three German officers of the submarine are now on their way to Donnington Hall and the men are in the temporary prison hulk moored up the river."

Before he returned to the Knat Lawless gloomily wrote a "chit" wherein he assigned to the skipper of the Cotswold his entire salary for the ensuing month.