Just then something happened. Darrin, using a trick that he had learned on the wrestling mat and had since perfected, threw both his arms around the left arm of the "Olga's" skipper. Clasping his hands and pressing his arms against the skipper's left arm, Dave gave a great heave and rolled to his own left. The trick depended upon speed. The skipper crashed over on his head. The revolver was discharged in the overturn, but the bullet went wild. In the twinkling of an eye Dave had grabbed the weapon, and leaped to his feet just in time to dodge the hatch bar that the mate tried to smash down on his head. "Back, unless you want yours right now!" Darrin challenged. Swiftly he changed the revolver into his left hand as he still covered the pair. Then he reached for his own automatic, throwing off the safety device. "Now, you, Mr. Mate, slip around and unbolt the door, throwing it open," Dave ordered. "Any sign of a trick will end your life on the spot!" Seemingly cowed, the mate obeyed. "Open the door--throw it wide open," Dave commanded. The door was thrust ajar just as the two seamen with the tape reached the bottom of the ladder coming from the deck. These two seamen stared in astonishment at the stuffy apartment off the after hold. "Men, take charge of these two rascals!" Darrin commanded, briskly. "Step lively, both of you!"--this last to skipper and mate, who obeyed as though dazed. "Pass them up on deck as prisoners," ordered Darrin, and this was done, the two seamen drawing their revolvers and standing by the "Olga's" discomfited officers. "Now, for your report," Darrin went on. One of the sailors reported the deck-length from hatchway to stern-post. "A difference of twenty-one feet," smiled Dave, darkly, pointing aft in the hold. "You see, men, there are a good many feet of length to be accounted for, which means that there is another compartment aft of this hold. You," turning to one of the sailors, "go forward and request Ensign Burton, with my compliments, to take charge of this steamer. He will round up the crew and place them under guard. Then the ensign will leave a petty officer in charge of deck and prisoners and report to me here." Within a very short time Mr. Burton had so reported. Dave, in the meantime, having worked his way over the cargo, had found a cleverly concealed door at the after end of the hold. "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. "Pass 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."