An unexpected "launch window" has provided the Robinsons with a golden opportunity to get off the planet. Unfortunately, time is of the essence--and right now time is running out thanks to a computer, residing in a tomblike cave, that has taken over Dr. Smith's (Jonathan Harris) mind and body, transforming him into an alien from a long-dead civilization. Will the Robinsons be forced to leave Smith behind in order to save themselves? ~ Hal Erickson, All Movie Guide