After a stint in Afghanistan, Officer Jenn Penton patrols Boston with a rare intensity and sense of purpose – particularly when it comes to getting drugs off the street. Meanwhile, Greg Dankers and the Fugitive Unit search for a drug dealer convicted of selling crack cocaine and gun ammunition in a Roxbury school zone.

The officers of the Boston Police Department live in the city they are dedicated to protecting, working to balance fighting crime with finding time for family. For the department's Gang Unit, the target is a well-known figure whose capture becomes personal. Meanwhile, the Fugitive Unit cases the streets of Charlestown for a local suspect wanted on charges in New Hampshire. And on-duty Patrol Officers drive through the city streets, encountering an assortment of characters and challenges on every shift.

The head of the police department's drug control unit decides there's only one way to stop the surge in drug violence plaguing South Boston: a massive raid on all the neighborhood’s biggest suspected dealers. It's a mission that will require tremendous manpower, careful planning, and perfect execution. Elsewhere, patrol officer Jenn Penton decides to try speed dating, despite her partner's skepticism.

In Dorchester, a string of gang-related shootings has the Boston Police Department on high alert. Things take a turn for the worse when a 20-year-old apparent gang member is shot execution-style in a local barbershop. With retaliation expected, the cops do everything they can to calm tensions and prevent another tragedy. Across town, the Fugitive Unit is on the trail of a dangerous knife-wielding robbery suspect.

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.

It's been a little over a year since gang unit officer "D" Araujo found himself staring at the wrong end of a gun while chasing a suspect. The experience continues to stick with him, particularly as he teams up with the SWAT team to capture a suspect who's believed to be involved in a series of gun battles in Mattapan. Meanwhile, over on the fugitive unit, Greg Dankers works days tracking down criminals while his wife Nancy, also a cop, works nights. With twin boys at home, that doesn't leave many openings for date nights, but he hopes to find time to cook her dinner after work.

Terrique Chambers didn't become a Boston police officer because it was an easy job. But after six years on the force, his work is - more than ever - at odds with his family life and his responsibilities at home. With two young sons, one of whom is autistic, the challenges of working nights in the gang unit are mounting. Meanwhile, his counterparts on the day gang unit are focused on something very different: the Boston Police Department's annual fitness challenge. They are determined to outperform their rivals in the fugitive unit. But Ryan Mason, Greg Dankers and company have a secret weapon in the competition, and they'll get an additional boost of momentum if they can first track down a dangerous suspect said to be hiding out in Dorchester.

Jenn Penton, one of the department's best patrol officers, is called upon day after day to solve one problem after another. But life doesn't always present issues that can be solved in short order. Her twin sister has been battling addiction for years. Now, after a few recent setbacks, she has reached out to Jenn for help – perhaps for the last time. Meanwhile on the fugitive unit, Winston DeLeon and company are pursuing a rape suspect from a case dating back to 1992. And Manny Canuto and "D" Araujo of the gang unit find themselves assisting in another SWAT raid, continuing their unrelenting quest to get as many guns off the streets as possible.