Det er nat med fru Knudsen

In a dilapidated little apartment in Vesterbro, Mrs. Knudsen lives with her incompetent and petty criminal son Arnold. Arnold's friend Benny also hangs out in the apartment at all hours, even though there is tension between the two companions. When a pretty girl accidentally rings the doorbell and ends up moving in, the battle between the two rivals breaks out into the open, and there is little room left for old Mrs. Knudsen.