Special government investigator Lee Barrett is sent to Station Three, a top-secret biological research installation in the desert, to investigate the disappearance of a flask which contains a newly-discovered virus known as the "satan bug" and of several flasks of botulinus organism. He learns from the general in charge of the investigation and from Dr. Hoffman, joint originator of the virus formula, that the satan bug is so virulent that if it were released in the atmosphere it could set off a chain reaction that would ultimately destroy all life on earth. Barrett eventually locates the stolen virus, but he and the general's daughter, Ann, are taken prisoner by Veretti and Donald, accomplices of Ainsley, a depraved millionaire who plans to use the virus to acquire power. Before the two accomplices are captured, they use some of the botulinus to wipe out a small community in Florida. Ainsley then threatens to destroy the entire city of Los Angeles with another flask of botulinus. Through frantic search efforts, the police find and disconnect the timing device which is set to spread the organism; but Ainsley remains at large with the flask of the satan bug. Barrett discovers that Ainsley and Dr. Hoffman are one and the same, and his pursuit of the madman climaxes in a struggle aboard a helicopter flying over Los Angeles. Hoffman falls to his death, and Barrett reaches safety with the flask of the satan bug still sealed.