To be honest and rather blunt, "The Parallel" is a very mundane and derivative TZ episode, but it just so happens to feature several themes and elements that are creator/writer Rod Serling's hobbyhorses. Serling seemingly can't get enough of space exploration, alternate dimensions, the continuum, etc. And since "The Twilight Zone" is entirely his party, we gladly indulge! Astronaut Bob Gaines returns seemingly unharmed from a mission in which he orbited several around the earth, but all contact with ground base inexplicably was lost for a period of six hours. Gaines notices very small differences with before he left, like a wooden fence in his front garden and an upgrade in his military rank from major to colonel. When also his wife and daughter notice "changes" in his persona, he openly wonders if he's not from another dimension. Unmemorable episode, but very watchable and easy to watch.