Dianetics guru Hubbard celebrates 50 years as a pro writer with this huge (800+ pages), swarming, sometimes gripping slug-lest. The Earth has been occupied by monsters, imperial Psychlos representing the Intergalactic Mining Corporation, who use ""breathe-gas"" (air is poisonous to them) and whose power derives from the closely guarded secret of teleportation. Furthermore, ambitious, devious Psychlo security chief Ted schemes to enrich himself by clandestinely mining gold, using humans as slave labor--and he is soon exploiting explorer-bravo Jonnie Goodboy Tyler (holding Jonnie's girlfriend as hostage). But Jonnie, learning that breathe-gas explodes on contact with radioactive materials, quickly amasses allies, arms, equipment, and expertise for a war of liberation: he plots to doublecross the snarling Terl by substituting nuclear bombs for the gold to be teleported to planet Psychlo. And that's only the first (definitely the best) installment in the struggle to free Earth. Future complications will include an internal fascist plot, war with several other alien races, and a wrangle with the Galactic bank (who claim that Earth is mortgaged for 40 trillion credits and intend to foreclose), before Jonnie and friends render the universe safe for social democracy. Pulp writing all the way--but, with reasonably tight plotting, furious action, and a mild comic strain (particularly where the various aliens are concerned): undemanding, have-at-'em entertainment for the sf/adventure set.