During the aftermath of the shooting from last season's finale (episode# 525), Mac takes the job of finding the gunman who shot at his colleagues personally and obsesses over the evidence. When Danny, who was left paralyzed in the shootout, tells Mac that he is going to meet a woman who seems to know the gunmen, Mac insists on joining him. When they arrive, the informant is hesitant to divulge information but lets on that her brother has some involvement and believes the gunmen are planning another shooting. Before she can tell Danny and Mac who she is, she is shot dead by one of the gunmen. The team pieces together what little evidence they have to find these gunmen before they kill someone else. When a nightclub becomes the shooter's newest crime scene, Mac realizes his team wasn't targeted by the gunmen; just at the wrong place, at the wrong time. When the gunman who shot their informant is found dead, the evidence trail leads the CSI's to the informant's identity, as well as her brother's and, ultimately, his fellow gunmen. Turns out they were three young men who devised a scheme to literally take NYC hostage, misguidedly believing they could force the city to pay them a ransom to stop the shootings.