Chicago Fire 4×18 “On The Warpath” – While responding to a call involving a victim incapacitated with a leg wound, Sylvie Brett (Kara Killmer) witnesses a murder and is threatened by the shooter not to go to the police. Unsure of what to do, she tries to track down Antonio (guest star Jon Seda) from Chicago PD. Elsewhere, Firehouse 51 jumps into action when a fire breaks out inside a restaurant, trapping several people inside a vault. Meanwhile, with his wedding day to Trudy (guest star Amy Morton) fast approaching, a nervous Mouch (Christian Stolte) starts to get cold feet. Jesse Spencer, Taylor Kinney, Eamonn Walker, Monica Raymund, David Eigenberg, Yuri Sardarov, Joe Minoso and Steven R. McQueen also star. Yaya DaCosta, Marina Squerciati and Miranda Rae Mayo also guest star.