Fred is caught and arrested by the police when his suit's invisibility function glitches during night patrol; the others have to break him out of the police transport.

A new villain calling himself Major Blast appears in the city and targets Fred; the other members of Big Hero 6 try to figure out who is behind the Major Blast mask.

Supersonic Stu busts his grandmother, Supersonic Sue, out of prison; at school, Professor Granville asks Wasabi, who fears public speaking, to sub for an absent teaching assistant.

Chief Cruz and the police get the upper hand in their battle with both villains and Big Hero 6 when they begin using Buddy Guardians, powerful new robots produced by Krei Tech.

Hiro and Baymax discover that Trina is trying to get revenge for Obake and cement his legacy by destroying the city; Big Hero 6 is forced to find a way to work with the police.

Hiro's friends show up late to a mission and his faith in them waivers; Hiro and Big Hero 6 try to stop Noodle Burger Boy and his new sisters.

Big Hero 6 responds to Richardson's every wish when he is made mayor for the day; Granville's three dogs go missing while under Hiro's watch.

Hiro switches Baymax and Mini-Max's chips so that Baymax can rescue Mochi; a low-charged Baymax and Mini Max must join forces with Noodle Boy to save Big Hero 6.

Hardlight crashes Karmi's autograph session for her new chibi series. Trini attacks the city using Krei's new automated vehicles!

Fred is attacked by mechanical cobras, but their target is a former spy who goes by the codename Mongoose; Fred meets the girls of his dreams, only to be rejected by her.

Members of a famous boy band decide to be crime fighters and challenge Big Hero 6 to a "superhero-off"; Go Go reluctantly goes under cover as the co-host of Wendy Wower's TV show.