When gang-related gunplay goes down in an emergency room, Horatio and the team must find the gang members responsible. The evidence suggests that an orderly in the hospital recognized the wounded gang member, who possibly killed one of the orderly's friends and alerted gang members to his location. However, the evidence doesn't match up and the CSIs discover that a cheating girlfriend, not gang retaliation, may be behind the shooting. Meanwhile, Ryan questions a mother in the emergency room after her story regarding her child doesn't add up.