A cop is shot while responding to a robbery, and later dies at the hospital. Frank then orders that everything be done to find the shooter. Danny investigates and gets second hand info on a suspect. He finds a witness who may have seen the shooter but is not sure. So they bring her to the station to look at photos but she fails to identify him, Danny does a little maneuvering to get her to say it’s the suspect. So he picks him up and puts him in a line-up. The witness is still uncertain. Erin tells Danny they don’t have enough. He, Henry, her boss and the whole department are upset with her. So much that cops who are suppose to testify say they’re unavailable. Frank upon learning this intervenes. But they are still unable to get the man they think shot the cop.