A small-town police officer, Tom Wachowski, discovers Sonic, a blue anthropomorphic hedgehog who can run at supersonic speeds. Sonic hails from another world and has come to Earth to escape forces that seek to harness his incredible speed for their own malevolent purposes. On Earth, Sonic enjoys his freedom but lives in secret, hiding from the townspeople and observing their lives from a distance, particularly fascinated by Tom, whom he idolizes. Unfortunately, Sonic's loneliness and longing for connection cause him to accidentally unleash a massive energy surge that knocks out power across the Pacific Northwest, drawing attention to his presence.

The U.S. government responds to the mysterious power outage by recruiting the eccentric and egotistical genius Dr. Robotnik to investigate. A master of robotics and advanced technology, Robotnik quickly discovers Sonic's existence and decides to capture him, planning to use Sonic's speed to further his own world-domination schemes. To evade capture, Sonic seeks out Tom for help. Despite being startled by Sonic's appearance and abilities, Tom agrees to help him. They embark on a road trip to San Francisco, as Sonic needs to retrieve his lost rings, which allow him to teleport to different planets. As they journey together, they develop an unlikely friendship while being relentlessly pursued by Robotnik, who uses an array of high-tech drones and weapons in his relentless pursuit to catch Sonic.