"What you have just witnessed could be the end of a particularly terrifying nightmare. It isn't - it's the beginning. Although Alan Talbot doesn't know it, he's about to enter a strange new world, too incredible to be real, too real to be a dream. It's called The Twilight Zone."
Alan Talbot seems to be an average man leading a seemingly normal life. He falls in love with a woman named Jessica Connelly. One day, he starts hearing strange noises that give him head pains and the urge to kill. As a result, he throws a religious fanatic under a train.
Upon visiting his home-town with Jessica, his memory seems to betray him. Nothing in the town is as he remembers. While seeking answers, he comes face to face with his double. It turns out that he is an android created in the image of Walter Ryder, provided with Walter's memories from twenty years before. Alan is the third prototype and has been "living" for eight days, as Walter had tried to create a less flawed image of himself. Unfortunately, Alan is insane and can't be fixed; he stabbed Walter with a pair of scissors before escaping.
Knowing what he really truly is, Alan tells Walter all about Jessica so that Walter can replace him, but he then malfunctions and tries to kill Walter. After the struggle with an ambiguous outcome, the survivor goes to Jessica in the morning, and is implied that the two will marry. In the final scene, it is revealed that the survivor is Walter while Alan lies amid the wreckage of the laboratory where he was "born".
"In a way, it can be said that Walter Ryder succeeded in his life's ambition, even though the man he created was, after all, himself. There may be easier ways to self-improvement, but sometimes it happens that the shortest distance between to points is a crooked line - through the Twilight Zone."