and cut jokes with each other with the utmost unconcern. The hoarse challenge "Boat Ahoy!" from the sentry on the "Pompey's" fore-bridge and the seemingly inconsequent "Aye, aye" of the picquet-boat's coxswain gave him an insight into the ceaseless vigilance of Britain's first line of defence.

Almost in a whirl he found himself ascending the accommodation-ladder and gaining the spacious quarter-deck.

"Eric, my boy!" exclaimed Mr. Greenwood delightedly, as his son, arrayed in unfamiliar garb, ascended the companion.

"By Jove! pater, what on earth brings you here?" inquired the A.P., astonished at the identity of his visitor. Then he paused, having become aware of the presence of the commander, who stood like a guardian angel behind the benighted visitor.

"Your father has told me that he wishes to communicate a matter of urgent importance, Mr. Greenwood," said the commander. "I think it would be well if you saw him in your cabin. If, in your opinion, the business is urgent, you will please report to me."

He moved away to consult with the officer of the watch before going below. Father and son stood irresolute; Mr. Greenwood hardly knowing how to begin, while Eric was beginning to wonder how and by what possible means could his parent possess a certain knowledge that would require to be reported to the commander.

Down the ladder and the half-deck Mr. Greenwood followed his son. Here an alert sentry drew himself up as the young officer passed. Then the stolidity of his face gave place to an amused expression as he noticed the dishevelled appearance of the A.P.'s companion.

"This way," continued Eric. "My cabin's under repairs. Haven't got it quite ship-shape after that little affair off the Belgian coast. I'll take you into Tressidar's cabin. Of course you know he's shipmates with me?"

He knocked at the metal door. Receiving an invitation to enter, he opened the door and drew aside a curtain. The cabin was small and brilliantly lighted. Over the closed scuttle a curtain had been drawn to make doubly sure that no stray rays were visible from without.

Seated in an arm-chair drawn close to a very small and compact stove was Sub-lieutenant Ronald Tressidar.

"I say, old man——" began Eric; then, noticing the look of astonishment in the sub.'s eyes, he broke off and followed the direction of Tressidar's gaze. For the first time he became aware of his usually precise parent's appearance.

Mr. Greenwood wore his coat buttoned tightly round his throat. The coat was literally caked with mud and dust and in addition was rent across the right shoulder. His face was as dirty as the proverbial tinker's; on his left cheek was a line of dried blood, the result of an unheeded scratch received in his tumble in company with the dead bush. His hair, generally sleek and well brushed, was tousled and matted with wisps of grass.

"Pater!" exclaimed Eric in utter amazement.

"It's all right, my boy," declared Mr. Greenwood reassuringly. "I've had the night of my life—absolutely. No, don't go, Tressidar. Listen to what I've discovered."

"Have a stiff glass of grog, sir?" asked the sub., after Mr. Greenwood had washed his face and hands and had smoothed his ruffled hair.

"Thanks, I could do with one," replied Greenwood, Senior. "In fact, I was on the point of asking for a whisky, only I thought from your look of astonishment that you imagined I had already had one too many. No, thank Heaven, I've got off lightly, but I've left my best umbrella on the beach."

"Fire away, pater," said Eric. "We are all attention."

Mr. Greenwood "fired away." Uninterrupted he pursued his narrative until he came to the discovery of the supposed derelict mine.

"It wasn't glass by any chance?" asked Tressidar.

"Glass?" repeated Mr. Greenwood. "Well, now I come to think of it, perhaps it did resemble glass. But why do you ask?"

"Because, judging by your description of its size and buoyancy, I am inclined to think that your mine was one of the glass buoys we use for marking the position of our submarine obstructions. After on-shore gales the coastguards find hundreds of them."