"Simpson!" cried Ned Newton, as he recognized the man who had been up the tree. "It's that spy, Simpson, Tom!" Chapter XII Bridging a Gap Such surprise showed both on the face of Ned Newton and that of the man who called himself Walter Simpson that it would be hard to say which was in the greater degree. For a moment the newcomer stood as if he had received all electric shock, and was incapable of motion. Then, as the echoes of Ned's voice died away and the young bank clerk, being the first to recover from the shock, made a motion toward the unwelcome and uninvited intruder, Simpson exclaimed. "I will not bother now. Some other time will do as well." Then, with a haste that could be called nothing less than precipitate, he made a turn and fairly shot out of the door by which he had entered the tank. "There he goes!" cried Mr. Damon. "Bless my speedometer, but there he goes!" "I'll stop him!" cried Ned. "We've got to find out more about him! I'll get him, Tom!" Tom Swift was not one to let a friend rush alone into what might be danger. He realized immediately what his chum meant when he called out the identity of the intruder, and, wishing to clear up some of the mystery of which he became aware when Schwen was arrested and the paper showing a correspondence with this Simpson were found, Tom darted out to try to assist in the capture. "He went this way!" cried Ned, who was visible in the glare of the searchlight that still played its powerful beams over the stern of the tank, if such an ungainly machine can be said to have a bow and stern. "Over this way!" "I'm with you!" cried Tom. "See if you can pick up that man who just ran out of here!" he cried to the operator of the searchlight in the elevated observation section of what corresponded to the conning tower of a submarine. This was a sort of lookout box on top of the tank, containing, among