"There should be a key to this door, sir," said Ensign Burton, "but if there is a key-hole we are unable to find it. If this really be a door it must be operated by a hidden spring."

"Perhaps an axe will work as well as either key or spring," Darrin suggested. "Pa.s.s the word for one."

The axe was brought by a heavily built seaman, who prepared to swing it against the door panelling.

"Break away the boards as gently as possible," continued Dave. "There may be an explosive device on the other side of the panelling. For that reason I'll stand by you, to take equal risk."

"If there is any risk, I'd rather you wouldn't take it, sir," urged the sailor.

"Thank you, but I'll stand by. Swing the axe," ordered Dave.

A few blows knocked in the panelling, revealing, beyond, a room of considerable size. Into this stepped the two officers, followed by the seamen with them. Unlike any part of the ship they had previously seen, this place was lighted by electricity. Burton found the switch, and turning it on, let in a flood of light.

"Sir, did you ever!" gasped the ensign.

The purpose of this room was all too plain. It was fitted with compressors, leading to a tube that left the ship under water. A small but powerful crane was in place over a closed hatchway. The latter, when opened, was found to lead down into a second hold, also electrically lighted. The two officers explored this second hold.

"Mines were kept here," Dave nodded, "and were hoisted above as needed.

They were dropped astern by means of a compressed air apparatus which, when the mine tube was open, kept the sea from entering. This ugly looking little steamer, outwardly a wood pulp carrier, is really a very capable mine-layer. She has been busy, too, on this cruise to England, but had sown all her mines before we overhauled her."

"It's plain enough, sir," agreed Ensign Burton.

"Confound this rascally skipper!" blazed Darrin, wrathfully. "While naval craft have been searching everywhere for submarine mine-layers, this skipper has been sailing openly on the seas and sowing mines right under the eyes of our allies! The accursed power of gold! This skipper, his mate and crew have been selling their very souls to the Hun for a bit of his miserable money!"

"They won't do it again, sir!" uttered Burton, grimly.

"Mr. Burton, you will remain aboard as prize officer, and take the 'Olga'

into the nearest British port and turn her over to the British Admiralty authorities. On receiving competent orders you will rejoin."

"Very good, sir."

"And now we'll hurry above and try to get hold of this ship's papers before any rascal has a chance to destroy them."

Boatswain's Mate Runkle had kept the officers and crew of the "Olga"

under such close guard that they were unable to get at their papers, which were quickly found by Darrin in the cabin to which he had first been invited on boarding the "Olga."

Out on deck, herded forward, were master and mate, seamen, engineers and stokers, a motley-looking outfit of twenty-one men all told.

"Bring that fellow here," Dave directed, coming on deck after having examined the ship's papers and then turning them over to Ensign Burton.

The master, purple-faced and ugly-looking, his eyes cast down, was brought before Darrin.

"Well, sir," announced Dave Darrin, eyeing the man grimly, "we have seen the cargo you have on board, and we have been able to judge the character of the cargo that you have dropped overboard."

The skipper started, but did not make any reply in words.

"How could you ever bring yourself to commit such villainy?" Darrin demanded, sternly. "You are not a German?"

"No," a.s.sented the other, shifting his weight from his right foot to his left.

"You are a subject of a neutral country."

"Dot is true," admitted the skipper.

"And yet, for hire, you and your men have been engaged in sowing mines, and have taken pay from Germany for your crimes."

"Mines? No! Ve do it not any. Ve never any had," declared the skipper.

"Tell that to an Admiralty court-martial," Darrin retorted. "You will have difficulty in clearing yourself. Fellow, you will find that you and your men will be charged with piracy, for you have been sowing death and destruction in the seas. Indeed, there can be no estimating how many ships you have already helped send to the bottom, no guessing how many lives your infamous work has cost. And you a neutral! Piracy!"

Skipper, mate and chief engineer turned pale at this significant speech.

The rest of the crew looked on in stolid wonder, for they understood no word of English.

"Vat? You proof it can't!" quivered the skipper.

"Wait!"

Dave gave Ensign Burton an order in an undertone. The ensign hurried to the bridge and almost immediately from the "Olga's" whistle a series of sharp blasts struck out on the air.

From the distance came an answering whistle. The "Olga's" whistle sounded again, and continued at minute intervals, until the outlines of another craft came up out of the mist and proved to be one of the mine-sweepers.

Dave had already reasoned out the probable course of the neutral country's freighter in the last hour before he had overhauled it. As the mine-sweeper slowly came abreast, Darrin, a megaphone at his lips, shouted an order for the course to be taken by his small helper, and added:

"Sweep thoroughly, and try to find some mines near by."

"Aye, aye, sir."

Within fifteen minutes a distant whistle came up from the fog.

"They've picked up one mine," Darrin announced.

Ten minutes later the sweeper's signal whistle was repeated.

"Two mines," he added, and the "Olga's" skipper shivered slightly.

Twenty minutes later came a whistle that was barely heard.

"Three mines," clicked Dave, and ordered the recall sounded, to be by direction signals at minute intervals.

"You make dot noise too much den have us all torpedoed yet," protested the "Olga's" skipper.

"If that happens, we have a rescue craft near at hand," retorted Darrin, meaning the "Grigsby," though the destroyer was now hidden by the fog.

"That was more than you knew when you planted mines to destroy vessels on the high seas."

"I did noddings do," growled the skipper.

In time the mine-sweeper came up into view, again reporting that she had picked up three mines by sweeping broadly over the course that the "Olga"

was believed to have taken. Then a junior officer from the sweeper came aboard with the measurements of the captured mines. These dimensions were quickly found to correspond with those of the planting device installed in the secret compartment of the "Olga."