Force field domes are put in place to protect cities, and a totalitarian global military government is established to effect the war and the survival of humans.

Thirty years later, Spencer Olham, a designer of top-secret government weapons, is arrested while on his way to work by Major Hathaway of the Earth Security Administration (ESA), being identified as a replicant created by the aliens.

Each has a powerful "U-bomb" in their chest in the exact design of a human heart, which can only be detected by dissection or a high-tech medical scan, since it only arms itself and detonates when it gets in close proximity to its target.

With the help of underground stalker Cale, Olham avoids capture and sneaks into the hospital where his wife Maya is an administrator to get the high-tech scan redone and prove he is not a replicant.

Hathaway thinks he has killed the true impostor, but as his men move debris away from the Centauri ship, the real Spencer Olham's body is revealed as well.

At that moment, Olham realizes aloud that both Maya and himself really are alien replicants, and the secondary trigger (his awareness of what he truly is) detonates his U-bomb, destroying himself, Hathaway, his troops, and everything else in a wide area in a fiery nuclear explosion.

When it was decided to expand the short into a feature-length film, additional scenes were written by Richard Jeffries, Ehren Kruger, and David Twohy.

[5] The site's critical consensus reads, "With its low production value and uninspired direction, Impostor comes off as a mixture of The Fugitive and Blade Runner, only not as good or as involving.

[7] James Berardinelli of ReelViews gave the film two-and-a-half stars (out of four), saying "there are a few moderately diverting subplots and the storyline eventually gets somewhere", but added that "Impostor wears out its welcome by the half-hour mark, and doesn't do anything to stir things up until the climax.