A dream sequence showcases slow-motion shots of the main characters, a collapsing horse, falling birds, butterflies, different planets, and images of the Earth colliding with a rogue planet.[9]
Part One: Justine
The dream belongs to Justine, who weds Michael in a castle owned by her brother-in-law John and her sister Claire. Justine and Michael are late for the reception due to their stretch limousine's difficulty traversing the narrow and winding rural road. Upon their arrival, Justine sees a star in the sky shining brightly. John, an astronomy enthusiast, explains it is the star Antares. The festivities are less than harmonious; Justine's divorced parents Gaby and Dexter verbally abuse each other in front of the guests. Justine, to John and Claire's annoyance, keeps wandering away. Justine's employer Jack, who announces her promotion to art director of his advertising firm, expects her to write a slogan for a new campaign during the celebration. Justine finds herself pushed into a role that others have chosen for her and falls back into depression, from which she has been suffering for a long time. Toward the end of the party, which goes on until the early hours of the morning, she quits her job in an argument and calls off her marriage to Michael after cheating on him. Early the following morning, while horseriding with Claire, Justine notices Antares is no longer visible in the sky.
Part Two: Claire
Some time later, Justine arrives at John and Claire's estate, having sunk even further into depression, where she struggles to leave her bed and is unable to eat. Antares's apparent absence is revealed to be due to a rogue planet, "Melancholia", which appeared from behind the Sun and passed in front of Antares, eclipsing it. John says that according to the scientists' calculations, Melancholia will pass in close proximity to Earth, but will not collide with it. Claire looks anxiously at Melancholia's path on the internet, learning of a theory that, having bypassed the Earth, it will turn back and collide with it. John tries to calm her down but secretly secures food and gasoline. In view of the approaching planet, Claire increasingly loses her composure, while Justine longs for the end of the world and "sunbathes" naked in the planet's glow at night.
Strange omens occur in the days that follow. The electricity in the castle goes out, the butler does not come to work, the horses in the stable are restless, St. Elmo's fire is seen at various times, and the weather changes erratically. Melancholia initially flies past Earth, seemingly vindicating John and the scientists. However, a gravitational interaction between the planets sends Melancholia across Earth's orbit for a second time, now moving on a path towards it. On discovering this, John takes his life by overdosing on pills. Claire hides his death from the family and attempts to flee with her son Leo, but the cars will not start. Justine declines to spend her final moments with Claire on the terrace by candlelight and wine. Instead, Justine calms Leo down by suggesting that they build a "magic cave" out of branches. Shortly before the collision, Justine, Claire, and Leo sit under the "cave" and hold hands. While Justine and Leo seem apathetic to, or at peace with, their impending doom, Claire panics and lets go, succumbing to her despair. Melancholia finally collides with Earth, engulfing them in a sea of flames as both planets shatter against each other.
