The SFIT students enter the warehouse to discover the place apparently abandoned, noting some kind of accident had occurred. But they also confirm this is all the work of Alistair Krei! Krei must be the thief after all!

Hiro has refitted Baymax with upgraded sensors to search for the evil thief. Finally, they find a data match and the SFIT "superhero" team sets out for battle to find the man in the mask and retrieve the microbots.

Hiro and the SFIT team join forces to become a fighting unit capable of taking on the man in the mask and the stolen microbots. Hiro makes upgrades to everybody's inventions and the others are amazed at how powerful they suddenly were! This was going to take some practice!

Baymax rescues Hiro and his friends as they ponder who the villain might be and how to catch him. Suddenly, Fred boldly proclaims he knows who the thief is!

Hiro discovers it was his friends from the Institute who were following him. When they see the redesigned, reprogrammed Baymax, they want to know what's going on. Before he could explain, they find out more than they might have wanted to know!

Baymax's reprogramming was complete. Hiro now had him transformed and ready to get the thief in the mask who stole Hiro's prized microbots. It was off to the warehouse to do the job. But when they arrived, things had changed.

Hiro spends the day out in the garage redeveloping Baymax from just a personal health care robot to a full size bot fighting machine capable to take on whoever it has stolen Hiro's microbots.

#Baymax inquires about Tadashi and Hiro tries to explain that Tadashi was dead, having perished in the fire. As he explains it was just an accident, the incredible thought comes to him -- maybe it wasn't an accident! Realizing the man in the mask was behind it all, he sets out to modify Baymax for his new mission!

Hiro and Baymax finally make their way safely back home. But what does he say to Aunt Cass? And how does he sneak Baymax back in without her knowing he was gone? And still, how is it his microbots survived the fire but seem to under the influence of someone else?

Hiro pursues Baymax flee the old warehouse after being chased by Hiro's own microbots he thought were destroyed in the fire. During the chase, Hiro spies a tall, dark figure in a white and red Kabuki mask lurking in the shadows. Could he be directing the microbots?