The film stars Onslow Stevens as a mad doctor whose serum turns a man into a catlike killer.

Two scientists on an expedition to the West Indies discover a serum which changes humans into cats, or, more precisely, into catlike killers.

[2] It was developed under the working title The Cat Man and was in production from the beginning of March 1948 to the middle of the month.

[1] According to a March 1949 Hollywood Reporter article, radio writer Joseph Ruscoll sued Edward Small for using the title of Ruscoll's radio show, The Creeper for the film.

[1] In a contemporary review, Dorothy Masters of New York Daily News described The Creeper as an effort "wasted in every phase, including story, performance and general production ... To further the bafflement, perfectly innocent people are given sinister mien.