He leaped back to the assistance of his brother, crooked his elbow about the stranger's neck, and dragged him back. The man struck out, wildly, twisted around and staggered Frank with a blow in the ribs. He managed to struggle to his feet, they saw his hand flash to his pocket, and then he produced a small package and flung it far out over the side. It had only taken a second, but that second was sufficient to serve for his undoing. Frank scrambled to his feet in the swaying boat, and for a moment they sparred. Then Frank's right fist shot out and the blow landed directly on the point of the stranger's jaw. The man was not knocked out, but he staggered back and the wild lurching of the boat sent him off his balance. He stumbled and fell. His head struck against the side of the boat and he crumpled up in a heap. The blow had knocked him unconscious. Frank bent over him. He saw that the man was not badly hurt, but that he had been stunned by the impact. He pointed out a coil of rope in the stern. "Tie his ankles, Joe, in case he wakes up. I've got to get back to the wheel." The _Sleuth_ by this time was off her course, and was wallowing in the trough of the waves. Quickly, Frank swung the craft about, but when he peered ahead to locate Bayport he gave an exclamation of alarm. The city was nowhere to be seen. The heavy cloud of mist that had been gathering over the bay now totally obscured the shores. How far the boat had departed from her course he did not know, and in the fog bank he had but a vague idea of their location. He began to look around in hopes of finding a compass, but there was none in the boat. "Have you got a pocket compass, Joe?" Joe, who was busily engaged in tying the unconscious stranger's ankles together, looked up and shook his head. "Isn't there one in the boat?" "No--and here we are in a fog bank. I don't know whether we're in the right direction for Bayport or not." CHAPTER XIII PAUL BLUM Frank Hardy reduced the speed of the motorboat, because he realized the dangers that lurked in the fog. Almost any moment they might crash into another boat in the bay. Even worse, they might be so far out of their course that they would pile up on one of the rocky shores. The fog was impenetrable. Frank did his best to judge their direction by the waves but this did not help greatly, as there were cross currents and the wind was shifting. The _Sleuth_ coursed on, feeling its way blindly through the haze that enveloped the bay. Frank peered ahead into the foggy veil. Joe concluded his ministrations to the stranger, who was now beginning to stir. The man opened his eyes and groaned. "Have you had enough?" asked Joe. "Who hit me?" "You hit your head against the side of the boat. Are you going to make any more trouble?" The man groaned again, tried to get to his feet, found that his ankles were tied together, and sank back with a sigh.