ton 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."

"Which proves, or doesn't prove, that the 'Olga' sowed the mines," Dave
declared. "That remains for the court-martial to decide. But the three
mines just swept up will be interesting evidence for the court to
consider."

Learning that the commander of the mine-sweeper would be glad to furnish
some members for a prize crew, and to convoy the prize into port, Dave
decided to leave Ensign Burton aboard with only three men from the
"Grigsby," filling out the prize crew with English sailors. This was
accordingly