the NBC show follows the lives of the firefighters and paramedics working at the Chicago Fire Department at the firehouse of Engine Company 51, Truck Company 81, Rescue Squad Company 3, Ambulance 61 and Battalion 25. Killmer, who joined in Season 3, announced in November that she would be leaving the series after a decade in the role of paramedic Sylvie Brett. Before leaving, though, Sylvie will tie the knot with Captain Matthew Casey (Jesse Spencer).