H.G. Wells' the Invisible Man

Four pilots have died in test flights of Professor Scott's fuel diffuser, a breakthrough that would more than double the range of current aircrafts. Scott is ready to admit defeat until Peter does some snooping around. The Invisible Man is convinced that it's espionage, especially after foreign agents try to assassinate him. He lets them think they've succeeded so he can root out the saboteur in Scott's lab.