3-Iron follows the trials and tribulations of an odd young man, Tae-suk (Jae), who spends his days putting flyers on people's doors just so he can check who hasn't taken them down after a day or two; believing those families to be away, he breaks into their homes and settles in for a while, cooking, cleaning, watching television, and sleeping, all done with an intoxicating charm. But one day he is caught by a troubled young woman, Sun-hwa (Lee), whose husband, Min-kyu (Kwon), abuses her mentally and physically; when the husband returns home, Tae-suk uses the man's 3-iron to hit golf balls at him. Sun-hwa then goes off with Tae-suk, joining him on his journey to empty houses. But when they walk into an apartment and find a man dead, their world changes despite their attempts to protect it.