In Sonic the Hedgehog 3, the peaceful life of Sonic, Tails, and Knuckles is disrupted when a mysterious black hedgehog named Shadow is awakened by G.U.N., a secret government agency. Shadow, a powerful creation from the long-abandoned Project Shadow, escapes captivity, confused about his purpose and haunted by memories of his lost friend, Maria Robotnik.
Meanwhile, Dr. Robotnik resurfaces, discovering Shadow and manipulating him into believing Sonic and his friends are enemies. Robotnik sets out to gather the Chaos Emeralds, ancient artifacts of immense power, to fuel his latest world-dominating scheme. Sonic and his friends embark on a race against time to stop Robotnik, clashing with Shadow in high-speed battles and uncovering the tragic truth behind his creation.
As the Chaos Emeralds’ energy destabilizes, threatening the planet, Shadow begins to question Robotnik’s motives. In a climactic showdown, Sonic and Shadow join forces to defeat Robotnik, with Shadow making a heroic sacrifice to save the world.
The film ends with Sonic and his friends reflecting on Shadow’s redemption, while a post-credits scene teases the emergence of Metal Sonic, setting up the next chapter.
