A Patch of Fog

Sandy developed a shoplifting addiction despite his successful career as a famous author. The movie doesn't explicitly explain the psychological cause, but his thefts appear to stem from a need for thrill or control, especially given that his creative output has been stagnant for decades.

Robert is a lonely, socially isolated man who sees his encounter with Sandy as an opportunity for genuine friendship with someone of higher social status. His obsession grows from a desperate need for connection and validation, making him unable to accept that Sandy views him as a nuisance rather than a friend.

Robert gives Sandy a coin that was flattened by a passing train, keeping the matching coin for himself. This symbolizes their 'bond' in Robert's mind, he views it as a token of friendship, but it actually represents his distorted perception of their relationship and his willingness to force connection.

The coins appear after Robert overhears Sandy calling him a 'sad little man,' establishing how disconnected their understandings of their relationship are.

Sandy breaks into Robert's apartment to find the disks containing evidence of his shoplifting. Unable to locate them quickly, he destroys the apartment in a frantic rage and throws the disks into the River Lagan, believing this will eliminate the blackmail material and free himself from Robert's control.

Robert had installed surveillance cameras in his own apartment, likely to monitor his belongings since he was blackmailing Sandy. After Sandy destroys the place and leaves, Robert retrieves the footage and sends it to Sandy, proving he knows about the break-in and further cementing his control over Sandy.

Robert is devastated to discover that Sandy not only broke into his apartment but also destroyed it and threw away the disks. He realizes Sandy never genuinely wanted friendship, everything was a manipulation to escape consequences. The revelation that his only 'friend' betrayed him so completely drives him to step in front of an oncoming train.

Robert discovers that the original handwritten manuscript of Sandy’s famous novel 'A Patch of Fog' was actually written by Robert’s own father. This reveals that Sandy has been a complete fraud his entire career, he stole another man's work and passed it off as his own, building his entire life and reputation on plagiarism.

Sandy admits he doesn't own a copy of his own novel and claims the original manuscript is somewhere in his house, hinting at its mysterious origin.

After killing Robert during a struggle over the manuscript, Sandy dumps his body into a lake and attempts to drive away. However, a rope from Robert's body becomes tangled around Sandy's ankle as he tries to leave, pulling him underwater. He drowns alongside Robert, making the ending a double fatality with no escape from the consequences of his actions.

Sandy initially agrees to meet Robert for drinks to avoid police involvement over his shoplifting. Later, he continues the pretense of friendship while trying to retrieve the compromising video disks, even getting Robert high on marijuana in hopes he would reveal where the disks are hidden. Sandy sees the relationship purely as a problem to solve, not a genuine connection.

When Sandy shows his video recording of destroying Robert's apartment to his university students, he frames it as 'performance art' and threatens to email the clip to all students. This is Sandy's attempt to weaponize his status as an author and academic, using the claim of artistic expression to humiliate Robert further and dismiss the criminal act as creative expression.

Robert breaks into Sandy's house after being publicly humiliated at the lecture and searches through the property. He finds the original handwritten manuscript of 'A Patch of Fog' and realizes the handwriting belongs to his own father, who died when Robert was young. This discovery exposes Sandy as a literary fraud who stole the novel.

Robert encounters Lucy, Sandy's girlfriend, while working his security job at the store. He introduces himself to her and her daughter Phoebe, seemingly seeking a connection to Sandy's 'normal' life. Later, when Phoebe drops something, Robert sees the deformed coin he gave Sandy, fueling his rage when he realizes Sandy has been carrying it as a trophy rather than a meaningful friendship token.

During the final confrontation in Sandy's house, Robert refuses to hand over the manuscript. When Robert tries to leave with it, Sandy grabs him in a headlock but loses his grip, causing Robert to fall and hit his head, dying from the injury. The killing is not premeditated, it's a desperate, violent act that spirals out of control during their struggle.

Sandy has all of Robert's furniture removed from his house and replaced with new furniture, keeping only the couch. This is his retaliation for Robert smashing his car windows earlier. By completely transforming the living room that Robert had decorated, Sandy destroys the space Robert had tried to personalize, while keeping the couch as a final taunt or trophy.