05/05/2015 (10:00PM - 11:00PM) (Tuesday) : TENSIONS BETWEEN SQUAD AND TRUCK BEGIN TO BOIL OVER THREATENING TO DIVIDE THE HOUSE, WHILE CASEY GOES UNDERCOVER- At Sgt. Voight's (guest star Jason Beghe) urging, a determined Lt. Casey (Jesse Spencer) agrees to go undercover in an effort to provide proof of Jack Nesbitt's (guest star Eric Mabius) shady dealings. Meanwhile, Otis (Yuri Sardarov) and Severide (Taylor Kinney) continue to disagree about the integrity of Scott Rice (guest star Warren Christie), causing tensions to flare between members of truck and squad. Meanwhile, Herrmann (David Eigneberg) helps out a fellow member of the firehouse. Jon Seda, Randy Flagler and Izabella Miko also guest star.