Apartment 12 tells the story of a Los Angeles artist whose life takes a sudden turn when an art curator cancels his upcoming one-man show and his model girlfriend leaves him. He is forced to move back to his old job at a pizza parlor and into a rundown tenement where he encounters several oddball characters.
These include a lonely middle-aged woman who makes Spam casseroles for the bachelors in the building, a daffy prostitute, and a Spanish Don Juan who wanders the halls in his bathrobe. Things start to look up when a young woman from Colorado moves in across the hall, but he soon realizes she has a total backwoods quality that he struggles to handle.
When he ends the relationship, the whole building turns against him, leading to a series of unexpected events.