"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 other machines, the searchlight. "Pick him up!" cried Tom. The operator flashed the intense white beam, like a finger of light, around in eccentric circles, but though this brought into vivid relief the configuration of the field and road near which the tank was stalled, it showed no running fugitive. Tom and Ned were observed--shadows of black in the glare--by Mary and her friends in the tank, but there was no one else. "Come on!" cried Ned. "We can find him, Tom!" But this was easier said than done. Even though they were aided by the bright light, they caught no glimpse of the man who called himself Simpson. "Guess he got away," said Tom, when he and Ned had circled about and investigated many clumps of bushes, trees, stumps and other barriers that might conceal the fugitive. "I guess so," agreed Ned. "Unless he's hiding in what we might call a shell crater." "Hardly that," and Tom smiled. "Though if all goes well the men who operate this tank later may be searching for men in real shell holes." "Is this one going to the other side?" asked Ned, as the two walked back toward the tank. "I hope it will be the first of my new machines on the Western front," Tom answered. "But I've still got to perfect it in some details and then take it apart. After that, if it comes up to expectations, we'll begin making them in quantities." "Did you get him?" asked Mr. Damon eagerly, as the two young men came back to join Mary and her friends. "No, he got away," Tom answered. "Did he try to blow up the tank?" asked Mr. Nestor, who had an abnormal fear of explosives. "Was he a German spy?" "I think he's that, all right," said Ned grimly. "As to his endeavoring to blow up Tom's tank, I believe him capable of it, though he didn't try it to-night--unless he's planted a time bomb somewhere about, Tom." "Hardly, I guess," answered the young inventor. "He didn't have a chance to do that. Anyhow we won't remain here long. Now, Ned, what about this chap? Is he really the one you saw up in the tree?" "I not only saw him but I felt him," answered Ned, with a rueful look at his fingers. "He stepped right on me. And when he came inside the tank to-night I knew him at once. I guess he was as surprised to see me as I was to see him." "But what was his object?" asked Mr. Nestor.