When a car plows through a crowd of concert goers and gunfire erupts, Lindsay and Ruzek are on the scene. Unsure of the motive and concerned a terrorist group may be responsible, Voight orders in Homeland security, customs and the F.B.I. to assist. At the same time, Burgess spots Atwater's brother, Jordan, out where he shouldn't be. The team use their connections to throughout the city to bring some peace to the community before more blood is shed.