Dr. Smith, Will and the Robot find a cave where they encounter shadowy beings who demand the Robot be given to them to examine. The three flee back to the Jupiter 2 where aliens project a message to Professor Robinson with an offer to buy the Robot, but he refuses to sell. When the aliens threaten to harm the family, the Robot voluntarily gives himself up for their experiment. The beings end up taking the Robot apart and then later dump his parts in a heap on the Robinsons' doorstep. Will rebuilds the Robot, but suddenly everything mechanical around the ship goes haywire. The Robot warns that the aliens are building a weapon that controls machinery and the Robinsons must stop their evil plans.