Season five of Chicago Fire, which follows the professional and personal lives of the men and women firefighters and paramedics working in the Chicago Fire Department, kicks off tonight. The heat is on in this steamy firefighting drama as tonight’s episode sees Severide (Taylor Kinney) and Stella (Miranda Rae Mayo) in danger when Stella's unstable ex-boyfriend Grant surfaces. Meanwhile, things take a dramatic turn when Borelli (Steven R. McQueen) files a grievance against Boden (Eamonn Walker) questioning his leadership following his brother's death. Also, Brett (Kara Killmer) discovers Mouch (Christian Stolte) is writing erotic fiction and agrees to help him out.