Costumed patients create a challenge for the doctors; Derek and Ben work on a new surgical technique; Richard asks a resident to perform his next surgery, angering Bailey.
Severide comes back to work, but isn't his usual self; Mills discovers more information about his father's family; Herrmann asks Molly investors to share ideas that could help turn the business around.
Ryan goes undercover in a white supremacist organisation to help stop the distribution of a deadly strain of tuberculosis. If he is unable to stop it in time, there will be deadly consequences.
A couple they barely know invites Jules and Grayson to their wedding, but the date conflicts with Grayson's roller-hockey final. Tom uses eerily lifelike dolls to make a model of the neighbourhood.
Leanne is warned to keep Ariel away from Max, and strives to save siblings who drank boiling water through a straw. Meanwhile, Mario arrives at the scene of a boat crash with Rox and Willis.