Synopsis by Hal Erickson
A race of shapeless aliens transforms themselves into exact doubles of the Robinsons, kidnapping the originals and reprogramming the Robot for evil. It is all part of a scheme to take over the earth with similar replicants. Escaping from their captors' clutches, Will Robinson (Billy Mumy) and Dr. Smith (Jonathan Harris) take the places of their lookalikes in order to foment dissension amongst the aliens and reclaim the Jupiter 2. The highlight of this episode is a side trip to Chicago, which though supposedly set in 1999 looks exactly like the Windy City of 1968!