Barry Nelson comes home from a business trip. His wife doesn't pick him up. He calls home, but she does not recognize his voice. He takes a cab, and finds his wife, his brother-in-law (his business partner), his dog (who bites him) and his exact double, who insists he is Nelson. They call a cop, but his ID has the other guy's fingerprints. The cop takes him to the police station, but a Doberman Pinscher attacks him and he flees in the confusion.
It's a very nice done movie version of a novel by Samuel W. Taylor. Director Edward Montagne keeps things going along at a good clip, with the doubling handled by a skilled combination of editing and masking by cinematographer Fred Jackman Jr.; there's also some good location shooting of San Juan, Puerto Rico. It's also Jack Warden's first credited role; he had had uncredited bits in three earlier movies.