It may be said with a degree of assurance that not everything that meets the eye is as it appears. Case in point: the scene you're watching. This is not a hospital, not a morgue, not a mausoleum, not an undertaker's parlor of the future. What it is is the belly of a spaceship. It is en route to another planetary system an incredible distance from the Earth. This is the crux of our story, a flight into space. It is also the story of the things that might happen to human beings who take a step beyond, unable to anticipate everything that might await them out there. Commander Douglas Stansfield, astronaut, a man about to embark on one of history's longest journeys - forty years out into endless space and hopefully back again. This is the beginning, the first step toward man's longest leap into the unknown. Science has solved the mechanical details, and now it's up to one human being to breathe life into blueprints and computers, to prove once and for all that man can live half a lifetime in the total void of outer space, forty years alone in the unknown. This is Earth. Ahead lies a planetary system. The vast region in between is the Twilight Zone.