While waiting in a bus station, Millicent Barnes has the strange feeling that her doppelganger is trying to take over her life.
Millicent Barnes, age twenty-five, young woman waiting for a bus on a rainy November night. Not a very imaginative type is Miss Barnes: not given to undue anxiety, or fears, or for that matter even the most temporal flights of fantasy. Like most young career women, she has a generic classification as a, quote, girl with a head on her shoulders, end of quote. All of which is mentioned now because, in just a moment, the head on Miss Barnes' shoulders will be put to a test. Circumstances will assault her sense of reality and a chain of nightmares will put her sanity on a block. Millicent Barnes, who, in one minute, will wonder if she's going mad.
Obscure and metaphysical explanation to cover a phenomenon. Reasons dredged out of the shadows to explain away that which cannot be explained. Call it 'parallel planes' or just 'insanity'. Whatever it is, you'll find it in the Twilight Zone.