Synopsis by Hal Erickson
No, the Robinsons' planet is not invaded by a group of 1960s pop singers. The titular fifth-dimensional creatures are a race of luminous aliens, in search of a new brain for their malfunctioning computer. When Dr. Smith (Jonathan Harris) is chosen to donate his brain, the cowardly physician declines the honor--and offers the brain of Will Robinson (Bill Mumy) as a suitable replacement. This episode incorporates some "jetpack" footage from the original Lost in Space pilot episode.