Of Unknown Origin is a 1983 thriller about an oversized rat that terrorizes a young executive's brownstone apartment. After Bart Hughes' (Peter Weller) wife Meg (Shannon Tweed) and his son leave for a short vacation, he begins to notice signs that signal he might have a mice infestation. After conventional methods such as rat traps and poison fail to work, Bart realizes that he's dealing with one large, menacing rat that is hell-bent on tormenting him. After reading books about rat infestations, consulting with exterminations and devising his own methods, the large rodent continuous to wreak havoc on his apartment. Not only is the rat crafty, but it also harasses Bart night and day and moves through his home at will. His battle with the rat soon affects his relationships and his work. Now that the rat has completely taken over Bart's home, he must devise unconventional methods to take it out.