This fourth volume of the complete children's sci-fi series includes a mission to foil evildoing aliens and a quick trip to eighteenth-century France. Norby and the Invaders Jeff Wells and his robot, Norby, must rescue the Grand Dragon of Jamya from strange, blimplike aliens known as the Hleno. Determined to protect the environment from the overuse of technology, the Hleno take Norby and Jeff prisoner, too. Encased in an impenetrable plastic bubble, Norby is helpless. And without Norby, Jeff is lost in outer space. Norby and the Queen's Necklace Sent to 1785, France, Jeff and Norby get mixed up with an extravagant necklace intended for Marie Antoinette—and accidentally alter events that led to the French Revolution. Now they must shuttle back and forth through time and space to set world history straight.