Jon Haljan pilots the Earth-Moon Mailship. While on vacation, he receives a startling message from Professor Grant requesting they meet, but not revealing why. When Jon arrives, he is greeted by Freddie Blake and his sister, Linda Blake. Informing the trio of the mission, Professor Blake tells the group he wants them to go to the planet Vulcan and retrieve "Uranium-X" to return with. The ship is prepared, and they leave on their mission.