Straight-laced and Up tight, FBI Special Agent Sarah Ashburn is just a systematic investigator with a reputation for excellenceand hyper-arrogance. Shannon Mullins, one of Boston P.D.'s"finest," is foulmouthed plus has a rather short fuse, also uses her gut instinct and streetsmarts to catch the very elusive criminals. Nobody has had somebody, or even a friend for that matter. Whenever these two law officers join forces to bring down a drug lord, then they turned into the final thing anyone expected: Buddies.