After more than a quarter century as a Boston cop and following a year filled with personal difficulties, Robert "Twitch" Twitchell is finally being promoted to Sergeant. Now, with just a week left as a detective in the gang unit, he's focused on bringing in one last perp. Meanwhile, it's a very different kind of week for Officer Myles Lawton with the approaching anniversary of the murder of his father, a former cop himself. The emotions are complicated by a frustrating Roxbury case in which the alleged shooter gets away, and no one seems to know anything about him.