One year following the tragic suicide of Vincent van Gogh, postman Joseph Roulin enlists his son Armand to deliver Vincent's final letter to his brother, Theo. Troubled by the circumstances surrounding Vincent's death—especially since he had communicated a sense of calm just weeks prior—Roulin is convinced that something is amiss. Reluctantly, Armand sets off for Paris to fulfill his father's request.
Upon arriving, he meets Père Tanguy, a local art supplier from Montmartre, who reveals a shocking detail: Theo had passed away six months after Vincent. This revelation leads Armand to Auvers-sur-Oise, where he hopes to seek out Dr. Paul Gachet, the doctor who had taken care of Van Gogh following his release from an asylum, shared a passion for art with him, and was present at the funeral. Unfortunately, Dr. Gachet is away on business, so Armand decides to stay at the same inn where Vincent had lodged. There he encounters Adeline Ravoux, the inn's temporary owner, who expresses her fondness for Van Gogh and her surprise over his untimely death.
Prompted by Adeline, Armand visits a local boatman, who informs him of Van Gogh's close friendship with Dr. Gachet's introverted daughter, Marguerite. However, when Armand approaches Marguerite, she adamantly denies any implication that an argument between her father and Vincent could have led to his suicide, expressing anger at the notion.
As Armand delves deeper into the mystery, he begins to suspect a local boy named René Secretan, who reportedly took pleasure in tormenting Vincent and was known to brandish a gun while intoxicated. Dr. Mazery, who had examined Vincent, corroborates Armand's suspicions, asserting that the gunshot must have been fired from a short distance, effectively ruling out the possibility of suicide. When Armand brings René into question, Marguerite admits that she shared a close, albeit non-romantic, bond with Vincent but remains unconvinced of René's capability for murder.
Finally, Dr. Gachet returns and agrees to deliver Armand's letter to Theo's widow. He confesses to having had an argument with Van Gogh in which Vincent called Gachet a coward for not pursuing his aspirations, leading to a heated discussion that resulted in accusations that Vincent's very dependence on Theo may have contributed to his worsening health. Gachet suggests this confrontation might have ultimately pushed Vincent to take his own life, believing it would relieve Theo of his burden. After Armand returns home, Roulin receives a letter from Johanna, Theo's widow, who expresses her gratitude for the return of the letter and includes a missive from Vincent himself, signed, "Your loving Vincent."
