One night, Big Hero 6 is on the search for a stolen shipment of nickel-titanium alloy. Hiro and Baymax track the shipment to a rundown warehouse. Hiro goes in alone and almost gets caught by a drone that is on patrol. He avoids it, but another one catches him, alerting Yama. He deploys a large robot named Mega Yama, made from the stolen metal, to attack Hiro. Pretty soon, Baymax and the rest of the team show up. At first, Mega Yama proves to be a tough robot to beat, but Big Hero 6 easily manage to disable it. However, Yama escapes, vowing revenge. Instead of going after him, the team decides to call it a night because famous alumni, Dr. Trevor Trengrove, will be making a special guest appearance at San Fransokyo Tech.
The next day, students are gathered to attend a science workshop hosted by Trevor Trengrove himself. Unfortunately, Hiro is not allowed to attend because he is under sixteen. So while his friends and Karmi partake at Trengrove's workshop, Professor Granville sends Hiro and Baymax, to the Sciencetoirum to attend a juvenile scientists workshop hosted by Wendy Wower, much to Hiro's dismay. Fred also attends, and while everyone is having a good time, Hiro stands around sulking. Wendy takes notice and has a talk with him. She reveals that she used to be a robotics major when she was a student at SFIT, and Trengrove was her lab partner, which surprises Hiro. Meanwhile, in Trengrove's workshop, things are looking suspicious for Go Go, Honey Lemon, and Wasabi. They notice Dr. Trengrove has been kicking out students who do not specialize in chemistry, physics or engineering. He even kicked Karmi out after mentioning she was a biology major. Now he is having everyone race against the clock to build piezoelectric generators. When Honey, Go Go, and Wasabi are the first to finish, Dr. Trengrove selects them to attend a special assignment.
Having grown weary of being in Wendy's workshop, Hiro gets permission to go and explore the museum, so he can look for a way to get into Trengrove's workshop. Hiro learns from Baymax, using him as a balloon hanging in the air, that Dr. Trengrove is taking Go Go, Honey, and Wasabi to another room in the warehouse. He also finds out that Yama is standing outside. Hiro and Baymax rush back to Wendy's workshop to get Fred. They are making model volcanoes, and this gives Hiro an idea. He gathers Wendy and the kids over to show their projects to Yama. Distracted, Hiro, Baymax, and Fred sneak into Trengrove's warehouse.
Back in Trengrove's workshop, Dr. Trengrove urges Go Go, Honey, and Wasabi to work on topics based on their majors. Honey makes a chemical compound for the lightweight protective exoskeleton, Wasabi builds a mega-pace projectile system, and Go Go builds a magnetic levitation system. Dr. Trengrove then takes their work to be evaluated, and while they wait, Hiro, Baymax, and Fred show up. When Dr. Trengrove returns, Yama shows up. It turns out that Trengrove has been working with Yama to build him a new improved Mega Yama, using the tech that Go Go, Honey, and Wasabi made. After Yama escapes with his new robot, Trengrove explains the alliance was built on blackmail. Yama has some incriminating information against him on a flash-drive, and threatened to expose it unless he cooperated. Big Hero 6 go after Yama and Mega Yama and arrive at the docks. With the tech made by Go Go, Honey Lemon, and Wasabi, Mega Yama proves much tougher to beat than before. It looks like they cannot stop Mega Yama, but then Hiro suddenly has an idea. Remembering the volcano project, Big Hero 6 stuff two chemical balls, filled with baking soda and vinegar, into Mega Yama. The two properties override Mega Yama's system, causing it to erupt.
Big Hero 6 arrives back at SFIT and present the flash-drive to Dr. Trengrove. Feeling rather guilty, however, he confesses to Wendy that he stole her thesis and wants to make things right by sharing the truth with the world. Rather than being upset, Wendy thanks Trevor for finally admitting the truth. She later takes a night tour of SFIT with Hiro; in during which, she reveals that Professor Granville was her mentor. This confuses Hiro, as he and the other students were told that Granville was an entirely new member of the staff, prompting him to look into the university's history. He finds a picture of Granville with a mysterious boy in a yearbook and begins to question her.
- Ryan Potter as Hiro Hamada
- Scott Adsit as Baymax, Astrophysics Major, Male Student
- Génesis Rodríguez as Honey Lemon
- Khary Payton as Wasabi
- Jamie Chung as Go Go Tomago
- Brooks Wheelan as Fred
- Haley Tju as Karmi
- Paul Briggs as Yama
- Jenifer Lewis as Professor Granville
- Kari Wahlgren as Brooke, Weird Little Boy
- Riki Lindhome as Wendy Wower
- Andy Daly as Trevor Trengrove
- At the end of the episode, Hiro mentions Tadashi Hamada Hall, which was seen in the end credits of Big Hero 6.
- Wendy examined Baymax just like Hiro did in the movie when he first met him.
- Her examination reveals that Hiro replaced Baymax's lithium ion batteries with supercapacitors, as he suggested to Tadashi in the film