Tae-suk (Jae Hee) is a loner who drives around on his motorbike, taping takeout menus over the keyholes of front doors and breaking into apartments where the menus have not been removed. He lives in those apartments while their owners are away, washing their clothes, mending their broken appliances, and taking selfies with their possessions. When he breaks into one large home, he is unaware that he is being watched by an abused housewife and former model Sun-hwa (Lee Seung-yeon). Tae-suk leaves after making eye contact with Sun-hwa, but then returns. He witnesses Sun-hwa’s husband Min-gyu abusing her and proceeds to catch his attention by practicing golf in the yard. He buffets Min-gyu with golf balls and then leaves with Sun-hwa.
Tae-suk and Sun-hwa begin a silent relationship, moving from one apartment to another, with Tae-suk occasionally practicing hitting golf balls by drilling holes in them, inserted a cord through the holes, and securing the cords with a knot around the bases of tree trunks. In one home, after drinking, they are caught by the returning owners, sleeping in their bed and wearing their pajamas. The male homeowner, a boxer, repeatedly punches Tae-suk. Later, Tae-suk practices hitting a golf ball tied to a tree, and the ball breaks loose from its cord, breaking through the windshield of a nearby car and brutally striking the car’s passenger in their head. Tae-suk, awash with guilt, is comforted by Sun-hwa.
The next night, Tae-suk and Sun-hwa break into a hanok, where they sit quietly, drink tea, and share a kiss. They later enter an apartment where they discover the dead body of an elderly man. They proceed to give him a proper burial. The following day, the elderly man’s son and daughter-in-law arrive at the apartment, and assume that Tae-suk and Sun-hwa killed him. Tae-suk and Sun-hwa are apprehended and interrogated by police, but remain silent. Tae-suk’s camera is confiscated, and the owners of the homes seen in the photos on the camera are contacted. The police learn that nothing was stolen from any of the houses, and an investigation reveals that the old man died of lung cancer. Min-gyu arrives to take Sun-hwa home, and bribes the policeman in charge of the investigation to allow him to strike Tae-suk with golf balls. Tae-suk ends up attacking the police officer and is sent to jail. There, he practices golf with an imaginary club and balls and develops his gifts for stealth and concealment, frustrating his jailers by remaining out of sight.
Tae-suk is released from prison, and Min-gyu prepares himself in case he returns for Sun-hwa. With his improved stealth, Tae-suk is able to rejoin Sun-hwa in her house, using his skills to evade Min-gyu’s detection. Sun-hwa appears to say “I love you” to Min-gyu and embraces him, but kisses Tae-suk over his shoulder. When Min-gyu leaves on a business trip, Sun-hwa and Tae-suk stand together on a scale. Text then appears, reading: “It’s hard to tell whether the world we live in is either a reality or a dream.”