Tom did not stop to answer, but quickly ascended the ladder. Ned, in a few words, told the others the alarming news that had come down from the cockpit, and then stood ready to carry out Tom’s orders. The young inventor, crowding into the narrow space of the after cockpit, found Wright managing the machinery, for the planes had a dual control system. In the forward cockpit Ted Dolan was slumped down in a heap. “What’s the matter?” cried Tom, when he reached Dolan’s side. “I don’t know,” the mechanician answered weakly. “It’s something I ate—or else I’ve been doped. My stomach seems caved in and I can’t see. I’ll have to quit, Mr. Swift—sorry——” “Don’t worry about that!” exclaimed Tom. “Ned and I can finish the trip—if the engine’s all right.” “But that’s just the trouble,” went on Dolan, in a weak voice. “She isn’t acting properly.” “Seems to be some obstruction in the oil feed line,” said Wright. “Use the other,” Tom promptly advised. “They’re both feeding slowly,” was the answer. “If the oil stops, we stop too!” Tom well knew that. “You get down to the cabin, Dolan,” advised the young inventor. “Mr. Damon will look after you—he’s a traveling medicine chest. But have you been eating or drinking with strangers?” “Nothing like that, Mr. Swift—no, sir! I only ate meals I was sure of, and at the hangar too. I never drank anything but water—not even sodas, for I know they can knock you out in hot weather. I think somebody got in the hangar and doped my food.” “It’s possible,” admitted Tom. “How about you?” he asked the assistant. “I’m all right—I can stick.” “Well, we may need you later. You go down now with Dolan and look after him, and send Mr. Newton up here.” Having given these orders, Tom began looking over the machinery. He was engaged in this when Ned came up to help, reporting that Mr. Damon was looking after the ill mechanician. “What’s wrong?” asked Ned. “Oil feed supply,” was the short answer. “You run the plane, Ned, and I’ll take the pipe down and clean it. We can run on one line while I’m working on the other.” It was a few minutes later, when Tom had the pipe uncoupled, that he uttered an exclamation of anger and surprise. “What is it?” cried Ned. Tom held out a piece of cork. It had been stuffed into the pipe in such a way that for a time enough oil would pass to keep the motors running, but the cork would gradually swell and eventually would completely clog the pipe, shutting off all oil. Without oil an engine will soon heat up, until, because of friction, the bearings, slide rods, pistons and cylinder walls may become red-hot. When that occurs the engine naturally stops. And when the engine of an aeroplane stops the plane falls. It is not like a dirigible that can sustain itself. “Dirty work!” bitterly murmured Tom, as he worked with all possible speed to replace the pipe, for the secondary oil supply was fast failing. The plane was losing speed rapidly.