In Tucson, a grandfather is shot after answering a knock at his front door. The suspect's getaway car crashes a few blocks from the crime scene and the suspect flees. Det. Bill Hanson and his team hope that clues from the car will lead them to the alleged killers. And in Cincinnati, an elderly man is found strangled to death in his bedroom. Det. Jennifer Mitsch and her team hunt for a strange man who was seen knocking on neighbors' doors just before the murder.