The episode features William Shatner in the lead role as a space explorer, not long before he was cast as Captain Kirk in Star Trek.
Until sometime in the last half of the twentieth century it is still a planet shrouded in mystery, enveloped in a heavy blanket of clouds and steam.
Because its surface temperature was believed to be several times that of Earth's, it was not thought possible for Man to reach Venus and come back... until one day, somebody did it.
"After completing the first crewed mission to orbit Venus, astronaut Jeff Barton returns to Earth with recurring nightmares and an increasing inability to stay warm.
Barton's doctors suspect the astronaut had been genetically affected by his mission, and they then struggle to treat and cure him before his mutations completely take over.