For the first time Harry Hazelton felt positively dismayed. He saw the long, massive arms moving, looking like a powerful ape's arms. There could be no doubt that the unknown was ready for a spring. Harry did not retreat. Where could he run to? Only a few yards could he go out towards the end of the wall. Then, if he wished to continue his flight he could only take to the water. Only a glance was needed at the bulky, powerful frame of the unknown to make it appear certain that the latter could swim two rods to the young engineer's one. Harry decided instantly to stand his ground and to make the most valiant fight possible on so slippery a footing as that presented by the top of the retaining wall. "Ha, ha! Ho, ho!" It was as though the black unknown sought to terrify his intended victim with his repetitions of that harsh, discordant laugh. Harry braced himself and waited. Then, off shoreward, came the sound of "put-put-put." The motor boat, "Morton," was putting out at last. "If I can keep this fellow busy for a few minutes, I can have all the help I want," flashed through Hazelton's mind. So he opened his mouth, raising his voice in a long, pent-up hail. "R e---e---e a d e! To---o---o---om R e a d e! Quick! Hazelton!" "Ha, ha!" jeered the unknown black. Then, suddenly, he leaped---not unexpectedly, however, for Harry had been watching, cat-like. The unknown threw out his arms, seeking to wrap them around Hazelton. Not in vain had Harry been trained, season after season, on the athletic ground of one of the best high school elevens in the United States. As the fellow leaped at him Harry crouched lower and went straight at his opponent. Powerful as the stranger was he was no football player. Harry "tackled" him in the neatest possible way, then strove to rise with this great human being. In the first instant it seemed to the young engineer as though he were trying to lift a mountain. His back felt as though it were snapping under a giant's task. Yet, but for one fact, Hazelton would have risen with his man, and would have hurled the mysterious one over into the waters of the gulf. Just in the instant of victory Harry's injured right foot gave out under him. With a stifled groan he sank down just as he threw his opponent. The black, instead of going into the water, landed hard on his back on the top of the wall. He was up again, however, before Hazelton could repress the pain in his foot and leap at the wretch. "Ha, ha! Ho, ho!" came the tantalizing challenge. "Put-put-put!" sounded over the water, coming nearer all the time. "Re---e---e---e a d e! T o m R e a d e! Help---quick!" yelled Harry, lustily. This, doubtless, was the first call that Tom, at the bow of the motor boat, thought he heard.