Picking up four months after the finale left off, Mac has left the force and is currently working for a lab that processes DNA recovered after the fall of the twin towers on 9/11. He's also spearheading the 9/11 memorial. Danny has become a Sergeant and Jo has begrudging taken over Mac's job on an interim basis. With the 10th anniversary of 9/11 upon us, each character re-calls where they were that day while simultaneously solving the murder of bar bouncer.