Two federal agents battle a gang that hijacks trucks carrying materials vital for the security of the country and sells them to foreign powers.

Man-woman team of investigators uncover a gang whose mad scientist leader has developed an invisibility chemical and plans to build a mercenary army of invisible men.

Mota is a Martian representative, who has come to impose interplanetary law on the Earth (which has become too dangerous); opposing his authority is Kent Fowler, who resists the alien plot, without understanding its details.