Agents of a foreign power are seeking to get possession of the plans of a new aeroplane motor invented by Dick Benton. Under cover of darkness they succeed in their scheme and are escaping in their automobile when it plunges over an embankment near Lone Point. The conspirators jump to safety just in the nick of time, and seeing an aeroplane from Dick's plant pursuing them they cut loose an engine in the yard and race away. When the aero arrives Helen boards it and the pursuit is taken up. The aviator arrives over the Melinus drawbridge before the engine, and Helen, having formed a daring plan, dives from the air to the waters of the river. She raises the drawbridge, thus forcing the conspirators to stop, and at the same time preventing a certain collision with the Limited approaching on the same track. The agents reverse the engine and speed back down the track, but Helen quickly lowers the bridge, and uncoupling the engine of the Limited gives pursuit and overtakes them.