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.
Ryan goes under cover to stop the distribution of a deadly strain of tuberculosis.
Jules and Grayson receive a wedding invitation but have conflicting plans; Tom has made a model of the neighborhood with eerily lifelike dolls.
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.
Mario joins Rox and Willis on the scene of a boat crash; Leanne works to save a brother and sister who drank boiling water through a straw as part of a challenge; Max's father tells Leanne to keep Ariel away from his son.
