Set in the summer of 1903, a series of unexplained events occur across the&nbsp;Eastern United States, caused by objects moving with such great speed that they are nearly invisible. The first-person narrator John Strock, &#39;Head inspector in the federal police department&#39; in&nbsp;Washington, DC, travels to the&nbsp;Blue Ridge Mountains&nbsp;of&nbsp;North Carolina&nbsp;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&#39;s&nbsp;<i>Robur the Conqueror.</i>)<br /><br />Robur has perfected a new machine, which he has dubbed the&nbsp;<i>Terror.</i>&nbsp;It is a ten-meter long vehicle, capable of operating as a&nbsp;speedboat,&nbsp;submarine,&nbsp;automobile, or&nbsp;aircraft. It can travel at the (then) unheard of speed of 150 miles per hour on land and at more than 200&nbsp;mph when flying.