A medical emergency brings Abby and Campbell’s friendship into focus and Abby reveals her biggest secret to Chris.

Edward and Carol Lynn wed, Danger Zone has their moment and Abby violates Chris’ one request.

At Sgt. Voight’s urging, a determined Lt. Casey agrees to go undercover in an effort to provide proof of Jack Nesbitt’s shady dealings. Meanwhile, Otis and Severide continue to disagree…