In the futuristic city of San Fransokyo, thirteen-year-old Hiro (Ryan Potter) has already graduated from high school, and now employs his genius to win underground robot wars. That is until older brother Tadashi (Daniel Henney) shows him around the ‘geek school’ where he studies robotics under the direction of top scientist Robert Callaghan (James Cromwell). Hiro decides that he must study there, and sets to work preparing a project for the forthcoming tech show that will be impressive enough for Callaghan to offer him a place at the university. His invention, ‘microbots’ – a mass of tiny robots that work together through a neurosensor to create whatever the mind envisages – not only impresses Callaghan, but also another key player in the science world, Alistair Krei (Alan Tudyk).
An elated Hiro is all set to join his brother at ‘geek school’ when a devastating event changes everything. Grief-stricken, Hiro falls into the care of his brother’s creation: Baymax (Scott Adsit), a giant inflatable healthcare robot. It soon becomes apparent, however, that there is something amiss in San Fransokyo and Hiro’s microbots are being employed for sinister means. Hiro and Baymax must join forces with fellow geeks Wasabi (Damon Wayans Jr), Go Go Tomago (Jamie Chung), Honey Lemon (Genesis Rodriguez) and Fred (T.J. Miller) to form a band of unlikely superheroes. Can this group of kind-hearted people, and a robot dedicated to saving lives, be ruthless enough to catch the masked villain and stop his reign of terror?