While rehearsing for a play, Will, Penny and Dr. Smith encounter a cosmic storm. A couple of strange artifacts in the form of a pair of gauntlets appear in the aftermath, followed shortly by a large hammer. Smith realizes the potential power of the objects and hides them, leaving replicas synthesized by the Robot in their place.
Later returning to the site, Smith is examining the objects when a creature appears and menaces him. He instinctively hurls the hammer at it and it is destroyed. This act of accidental bravery summons the Valkyrie Brynhilda to the planet and she tells Smith that he has demonstrated his worthiness to replace Thor as the protector of Valhalla. Lured by the promise of riches and power, Smith returns to Valhalla with Brynhilda.
Will witnesses their departure, but when no believes his story, he and the Robot return to the place where they last saw Smith. With the help of one of the gauntlets that was dropped by Smith, they are able to journey to Valhalla. There they find that Thor is furious over Smith’s usurpation of his leadership. When he discovers that Smith has lost one of his gauntlets, he casts him down into Niflheim where he is tormented by elves and threatened by a dragon.
After being released from Niflheim, Smith manages to convince Thor of his inadequacy. He is so successful that when the frost giants attack, Thor is unable to meet the challenge, and Smith, of course, lacks the courage to do so. Only by Will’s pep talk is Thor’s confidence restored. He does battle with the frost giants and triumphantly returns to Brynhilda.
Will, the Robot and Doctor Smith are all sent back home. Smith is thrilled to see a treasure chest has been sent along with them, but his joy is short-lived when he opens it—it contains no treasure.
- Sheila Mathews Allen, or Sheila Allen who played the female viking, was Irwin Allen's wife.
- In one scene Dr. Smith is hiding under a bearskin rug in Thor's lair. When Thor finds Smith Thor says: "I've got you under my skin."
- Doctor Smith thinks that there is a cosmic storm, because he wrote it into the third act of his play. Is he really that silly?
- Considering the Jupiter 2 has such limitations on weight and cargo, how did Smith plan on taking his many chests of treasure with him when they took off?
- Since when can the Robot replicate things? Why was this amazing ability never used before, such as in the episode “Blast Off Into Space,” when they needed a thruster control unit?