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 done. Dave's own ship was then signalled and located by whistle, and the launch started on its return. "Keep that captured crew under strict guard. Don't give them any chance to recapture their vessel!" was Dave's last warning to Ensign Burton. The "Olga" quickly faded away in the fog and then the "Grigsby" was picked up and boarded. "Great work, sir, I'd call it!" declared Lieutenant Fernald, when he heard the details of what had taken place. "The scoundrel, to sail as a neutral, and do such dirty work for the Huns for mere pay!" uttered Dave, indignantly. "Fernald, do you know that there were moments when I had to restrain myself to keep from kicking that scoundrel about his own deck?" "I can understand the temptation," nodded the executive officer. "On second thought, though," Darrin continued, "the skipper is certainly being much worse punished by the suspense of mind in which his present plight places him. He knows that, if convicted, the finding of the court will be 'piracy,' and he knows the punishment for that crime." "It used to be hanging," nodded Fernald. "It seems almost a pity that this war has introduced the swifter and more merciful punishment of death by shooting." "And as he looks around at his crew he knows that they must face the same fate with him, and he knows, too, that they know that he has brought the penalty upon them." "But is it possible that the crew were ignorant, or most of them ignorant, of what he was doing in addition to really carrying wood pulp cargoes?" asked Fernald. "That will be another question for the court-martial to decide," Darrin answered. "It doesn't seem possible that any member of the crew could really be in ignorance of the mine-laying work." A long blast from either the invisible "Olga" or the equally invisible mine-sweeper now announced that the prize was proceeding on her way. The "Grigsby" did not answer, for on a sea infested by hidden enemies it was not wise to use too many whistle signals.