影片故事设定在一个融合东西方文化（旧金山+东京）的虚构大都市旧京山（SanFransokyo）中，一位精通机器人技术的小神童滨田广（Hiro Hamada）发现，这座充斥高新技术的城市正遭遇着一场犯罪危机，为了拆穿阴谋拯救家园，他将携伙伴机器人Baymax，与一伙生拉硬凑的菜鸟团队组成“六大英雄”联盟，共同作战抗击罪恶。
Protagonist Hiro Hamada is a 14-year-old robotics genius who lives in the futuristic (fictional) city of San Fransokyo and spends his time participating in illegal robot fights; to amend which, his older brother Tadashi takes him to the robotics center at his university, where Hiro meets Tadashi's friends: GoGo, Wasabi, Honey Lemon, and Fred, as well the healthcare robot Baymax that Tadashi created. To enroll in the school, Hiro presents microbots: swarms of tiny robots that can link together in any arrangement imaginable — to Professor Callaghan, the head of the school's robotics program. When a fire breaks out at the university, Tadashi rushes in to rescue Callaghan, but both are killed, and Hiro secludes himself. ...