A warlord from Mars recruits an Earth industrialist with a Nazi past to manufacture weapons by means of which Mars can take over the Earth. Feature version of the 1951 movie serial "Flying Disc Man from Mars".

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.

Magazine writer Ann Mason infiltrates the United Defenders, a public service organization which is actually a front for racketeers. But a case of amnesia threatens to blow her cover.