An undisclosed Asian government plans to take over America by infiltrating and substituting officials at the
White House. During the presidential campaign, William Lyons Selby, the candidate predicted to win the election, is murdered and replaced by a
lookalike. Selby is indeed elected, and the impostor assumes the office of
President of the United States. Though "Selby" fools the nation at large during his first few months in office, his daughter, Carol, soon begins to suspect that the man in the President is not her father. She observes that "Selby" remembers dates and other publicly available information, but forgets private information, such as his food preferences and details of her husband's research projects. Carol voices her concerns to the
Vice President, Ted Pearson, who disbelieves her until he is targeted for replacement by an assassin resembling Pearson who breaks into his residence, is discovered
lying in wait, and is chased off before he can effect the replacement. Carol's husband, a physician and medical researcher, recalls that a peer-reviewed scientific journal disclosed
Soviet experiments wherein a
hominid animal's soft tissue had been successfully altered, and he speculated that the "serum" which was employed had been advanced significantly beyond that which was previously disclosed, to include human subjects, and he explains this to the Vice President. Now convinced that Carol's expressed concerns are plausible, Pearson informs Frank Summers—the head of the
Secret Service detail assigned to the White House—of the plot, and his suspicion that "Selby" is actually an impostor, but Summers' team fails to confirm "Selby's" true identity using
forensic science. Prior to a planned summit meeting, the leader of the Asian government confers with "Selby", wherein he reveals the second phase of his conspiracy—to replace various members of the
Cabinet and numerous industry leaders in order to complete his takeover of America. When "Selby" arranges a second attempt at replacing the Pearson, the conspirators, including Pearson's
doppelgänger, are captured, brought before a state reception, and, along with "Selby," are publicly exposed, with the real Pearson placing the lookalike under arrest, but not before permanently disfiguring him by using the formula. Summers proposes an armed response against the Asian government, but Pearson, now as President, declines. ==Closing narration==