Urbania follows Charlie through a sleepless night. After an unsuccessful bout of masturbation to the sound of his upstairs neighbors having sex, he prowls the streets searching for a man he saw several months earlier—a man whose connection to him hints at a one-night encounter that could have affected his relationship with his boyfriend, Chris. He places several calls to Chris, leaving messages on the answering machine as he moves from shadows to streetlight, trying to explain his actions even as the night stretches on. As he walks, he experiences brief, dreamlike flashes: a man's mouth, a bottle breaking, a man in a blood-stained shirt. These images blur the boundary between waking and dreaming, tugging at the edges of reality.
After a series of encounters—with his upstairs neighbors, whom he confesses to about his private activities, and with a potential sex partner—he finally meets the man he has been seeking. The man is Dean, and the dynamic between them grows increasingly unsettled and uncertain. It becomes clear that it would make little sense for either of them to pursue sex, yet the tension persists. [Charlie] pretends to be straight, buys Dean drinks, and shares a joint. Dean leads him toward a gay cruising area in search of victims, but Charlie manages to warn away the intended target. Dean becomes almost incapacitated by alcohol and drugs, and Charlie helps him into a car, driving him to a secluded marshy area.
As the past implied by Charlie’s flashbacks unfolds, it is revealed that Dean and two of his buddies attacked Charlie months earlier, raping and murdering Chris in what appears to be a hate crime. Charlie’s purpose becomes clear: revenge.
In a dreamlike conversation with Chris, Charlie recounts what happened at the marshland. He pulls a knife on Dean and explains why he is there. Dean does not remember him. Charlie forces Dean to drop his pants and is revolted to see that Dean has an erection. He forces Dean to kneel and perform oral sex on the knife blade. Suddenly, Dean collapses with an epileptic seizure, and Charlie slits his throat.
Chris challenges Charlie, not believing that he killed Dean. Charlie admits that he wanted to, but could not bring himself to complete it. Instead, he drives off in Dean’s car, leaving him in the marsh.
He stands up from where he has been kneeling, at a makeshift memorial near where Chris was killed. He walks home and experiences one final hallucinatory flash: he sees himself on the street, cradling a dying Chris. He kisses Chris goodbye and passes by him; when he turns back, Chris is gone. Charlie makes it home and, at last, is able to sleep.
Charlie presents his story in the form of urban legends, and the film references a number of these legends both through characters describing them as they are depicted and by showing ordinary people encountering them.
