His father sanctioned the plan of going to the rescue in one of Tom's several airships and, Mr. Damon, having been on hand, at once agreed to go. Of course Ned went along, and they had picked up the private detective in New York, where he was vainly seeking a clew to the whereabouts of Mr. Petrofsky. Now the young inventor and his friends were hovering over the sandy stretch of coast that extends from Sandy Hook down the Atlantic seaboard. They were looking for a small fishing hamlet on the outskirts of which, so the Russian letter stated, was situated the lonely hut in which Mr. Petrofsky was held a prisoner. "Do you think you can pick it out from a distance, Tom?" asked Mr. Damon, as the airship floated slowly along. It was not the big one they intended taking on their trip to Siberia, but it was sufficiently large to accommodate the four and leave room for Mr. Petrofsky, should they succeed in rescuing him. "I think so," answered the young inventor. In the letter from Russia a comparatively accurate description of the prisoner's hut had been given, and also some details about his guards. For there is little goes on in political circles in the realm of the Czar that is not known either to the spies of the government or those of the opposition, and the latter had furnished Tom with reliable information. "That looks like the place," said Tom at length, when, after peering steadily through a powerful telescope, during which time Ned steered the ship, the young inventor "picked up" a fishing settlement. "There is the big fish house, spoken of in the letter," he went on, "and the Russians know a lot about fish. That house makes a good landmark. We'll go down now, before they have a chance to see us." The others thought this a good idea, and a little later the airship sank to the ground amid a lonely stretch of sand dunes, about two miles from the hamlet on the outskirts of which the prison hut was said to be located. "Now," said Tom, "we've got to decide on a plan of campaign. It won't do for all of us to go to the hut and make the rescue. Some one has got to stay with the airship, to be ready to start it off as soon as we come back with Mr. Petrofsky--if we do come. "Then there's no use in me staying here," spoke Detective Trivett. "I don't know enough even to turn on the gasolene." "No, it's got to be Ned or me," said the young inventor. "I'll stay," volunteered Ned quickly, for though he would very much have liked to be in at the rescue, he realized that his place was in the airship, as Mr. Damon was not sufficiently familiar with the machinery to operate it. Accordingly, after looking to everything to see that it was in working order, Tom led the advance. It was just getting dusk, and they figured on getting to the hut after dark. "Have everything ready for a quick start," Tom said to Ned, "for we may come back running." "I will," was the prompt answer, and then, getting their bearings, the little party set off.