Set in the summer of 1903, a series of unexplained events occur across the eastern United States, caused by objects moving with such great speed that they are nearly invisible. The first-person narrator John Strock, 'Head inspector in the federal police department' in Washington, DC, travels to the Blue Ridge Mountains of North Carolina to investigate. He discovers that all the phenomena are being caused by Robur, a brilliant inventor. (He was previously featured as a character in Verne's Robur the Conqueror.)Robur has perfected a new machine, which he has dubbed the Terror. It is ten-meter long vehicle, capable of operating as a speedboat, submarine, automobile, or aircraft.