A flying saucer arrives on Earth while searching for planets suitable to raise “Gargons”, a lobster-like but air-breathing monster that is a reserve food supply on their home planet. Crewman Thor shows his alien contempt for Earth’s creatures, by needlessly vaporizing a dog named Sparky with a disintegrator raygun. Another crew member by the name of Derek, discovers an inscription on Sparky’s dog tag and fears the Gargons might destroy Earth’s native inhabitants. This makes the other aliens scoff at the thought. Being members of the “supreme race”, they disdain “foreign beings”, no matter how intelligent; they pride themselves that “families” and “friendships” are forbidden on their world. Derek reveals an ancient book and turns out to be a member of an underground rebellion, that commemorates the more humane periods of their world’s history, before they became mechanized slaves. Asking for the book, the Captain and Thor disarms Derek. Taking him as prisoner, they plan to put Derek on trial and have him executed by the high court. The Gargon they brought with them suddenly falls sick to Earth’s atmosphere. While his crew members are distracted, Derek escapes on foot. Eventually, the Gargon revives from being unconscious. When the Captain gives his report, it is revealed that Derek is the son of the Leader of their race, although he is unaware of this. Thor is sent to hunt down Derek, with orders to bring him back alive or kill him and any other intelligent beings to protect their mission to Earth. The rest of the crew return to their home world, leaving the Gargon behind in a nearby cave.