The story follows Holly Gooding (Drew Barrymore), who moves from New York City to Los Angeles after being implicated in a murder.

While in Los Angeles, she finds a room for rent by a writer named Patrick Highsmith (George Newbern).

When Patrick finds out that Holly's mother was murdered and she is the prime suspect, he starts doubting her sanity.

At the end it is revealed that Holly has a split personality and absorbed a vanishing twin as a fetus in the womb.

Avi Nesher wrote Doppelganger as a deliberately smaller scale film after production stalled on a large scale science fiction film called Hammerheads he was to write and direct with the project eventually being cancelled.