10/01/2013 (10:01PM - 11:00PM) (Tuesday) : THE THREAT OF AN ARSONIST WITH A VENDETTA AGAINST THE FIREHOUSE LOOMS AND CASEY STRUGGLES WITH THE REPERCUSSIONS OF HEATHER DARDEN'S ACCIDENT - In the wake of Heather's (guest star Chaon Cross) incident, Lt. Casey (Jesse Spencer) is having a hard time handling his newfound responsibilities. Lt. Severide (Taylor Kinney) is on edge dreading the next attack from the firehouse's arsonist. Meanwhile, with Renee (guest star Sarah Shahi) back from her mother's, Severide knows he has to confront her about his paternity suspicions. Elsewhere, Mouch (Christian Stolte) begins his campaign for union president and Shay (Lauren German) and Dawson (Monica Raymund) feel that they need to get out more. Eamonn Walker, Charlie Barnett, David Eigenberg, Yuri Sardarov and Joe Minoso also star. Treat Williams, Michelle Forbes, Jon Seda, Jesse Lee Soffer and LaRoyce Hawkins also guest star.