Of Unknown Origin

Of Unknown Origin is a 1983 psychological horror film directed by George P. Cosmatos in his North American film debut, and starring Peter Weller, Jennifer Dale, Lawrence Dane, Kenneth Welsh, Louis Del Grande and Shannon Tweed in her film debut. Based on the novel The Visitor by Chauncey G. Parker III, it focuses on a mild-mannered Manhattan banker who becomes increasingly obsessive and destructive in his attempts to kill a rat loose in his renovated brownstone. The film's title refers to the misconception that rats have no known origin.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.