Arthur, a quiet and unassuming man working as a shipping clerk at a bath fixture factory, navigates a deeply fractured reality. Trapped within a mundane existence in a small town, Arthur harbors severe psychological trauma rooted in a deeply
troubled childhood. His life seems deceptively normal on the surface, punctuated by mandatory sessions with his court-appointed therapist, Dr. Warren, and a blossoming, innocent crush on Fiona, a vibrant British accountant who works in the same building. However, Arthur’s internal world is a chaotic battleground governed by two distinct auditory hallucinations: Mr. Whiskers, his foul-mouthed, hedonistic pet cat who constantly eggs him on toward impulsive and destructive behavior, and Bosco, his endlessly optimistic, moralistic golden retriever who urges him to be good and do the right thing.The narrative takes a dark, irreversible turn after Arthur misses a company-sponsored bowling night and instead offers Fiona a ride home after her car breaks down. During the rainy drive, a startled deer jumps through the windshield, leaving the animal severely injured and suffering. Panicked and desperate to end its misery, Arthur uses a hunting knife to kill the deer. Terrified that Fiona will scream and expose his unstable state, he accidentally slashes her throat. In a state of catatonic shock, Arthur listens as Mr. Whiskers convinces him to bring Fiona’s body back to his apartment to "keep her company," while Bosco frantically begs him to confess.Back home, Arthur dismembers Fiona and places her talking, disembodied head inside his refrigerator, where it quickly becomes his primary confidante. Rather than feeling immediate guilt, Arthur spirals further into psychosis. He stops taking his antipsychotic medication, which causes Mr. Whiskers and Bosco to vanish from his auditory landscape, leaving his apartment eerily silent and forcing him to confront his rotting reality. Driven by a desperate need for female companionship and validation, Arthur sets his sights on Lisa, one of Fiona’s compassionate coworkers. Despite his awkward charm, Lisa becomes unnerved by his bizarre behavior and ultimately discovers the truth when she breaks into his squalid home, stumbling upon the preserved remains of Fiona and another victim, Alison.Cornered, Arthur accidentally kills Lisa as well, adding her head to the horrifying collection in his fridge. As the police finally close in on him, SWAT teams breach his apartment, leading to a fiery confrontation that burns the building down. Miraculously surviving the inferno, Arthur is placed in a psychiatric facility. In a surreal, transcendent musical finale in the afterlife, Arthur is reunited with Fiona, Lisa, Alison, and his deceased parents, finally finding peace, forgiveness, and
unconditional love among the ruins of his tragic, fractured mind.