I have only the vaguest recollection of this one. Apologies in advance for the scanty description and any potential inaccuracies in the details.
As best as I can recall, the story centers around a doctor or a scientist of some sort who is in great danger. He reaches out to a woman for help. I believe he's convinced that there is a conspiracy afoot and "they" are after him.
I am not certain if the story was supposed to be set in the future or near-future, though it may have been.
The woman assists, and I believe a romantic bond blossoms between them during their escape efforts. Unfortunately, near the end the two are caught. It is at that point the twist in the story is revealed.
The people chasing after the man are in fact doing so at his behest. For whatever reason, the person he seems to be is not his true self. He's actually a very selfish and cruel sort, and established a fail-safe in case he went rogue.
The story ends with him being restored to his former malevolent personality, and I believe the woman meets some sort of unpleasant fate.
I only remember that it was an episode of a television series, and was in color. There was closing narration on the story, leading me to believe it might be from one of the later versions of The Twilight Zone or The Outer Limits, but I don't remember enough of the story for my Google-fu to be of much use.