Dr. Alexander Kline, a biological scientist, views his work as evil, and to prove it, he plans to unleash a deadly germ that would kill thousands. Three dead cows lead McGarrett on a desperate chase to track down the toxin, involving a friendly telephone operator and top Washington agents.

Dr. Kline's deadly toxin is lost, he is having second thoughts about his plan, and McGarrett has to find the vial before it disintegrates and poisons the whole island. Already the toxin is doing its deadly work as innocent people come into contact with it.