When Danny is put on modified assignment after an incident in which a cop--who failed to identify himself--is shot, he faces Internal Affairs investigators, who are looking to his state of mind on that day for further implications.

Frank deals with a political crisis after Jamie and Renzulli are injured by a church security team that refuses to let them enter a religious center in response to a 911 call.

Frank must race to stop a biological weapon attack on New York City, while keeping it a secret from his family during their most sentimental holiday, Mother’s Day. Meanwhile, a long-standing conflict between Danny and Jamie comes to a head.

A dangerous criminal from Danny's past comes back to seek revenge and kidnaps Jackie. Meanwhile, Jamie meets his new partner, while a young officer is shaken after he accidentally shoots an innocent man.

Danny and Jackie set out to investigate the murder of a bride on her wedding day in a drive-by gang shooting. However, they are pulled off the case and assigned to the protection detail of a Central American president, who they believe is a target for assassination. Meanwhile, Jamie questions his partner Vinny’s methods when he performs an unjustified stop.

Danny arrives at a college campus to find a murdered student, who was thought to be dealing drugs. Meanwhile, Jamie has a life crisis when he reconnects with a former law school classmate and Erin must learn to give Nicky some freedom.

When two motorists driving gas-guzzling cars die at the hands of a sniper, Danny and Kate are put on the case of what the city believes is the work of a radical environmental serial killer. Meanwhile, a bicycle accident sends Danny’s son Sean to the hospital with a life-threatening injury.

When a devoutly religious young woman is found murdered in a cemetery, Danny questions her family who is shocked to learn that she had a secret relationship.

As the Reagans rally together to take down the leader of the gang responsible for the murder of someone close to them, Danny looks to the gang leader’s girlfriend to lead them to him. Meanwhile, Frank is left reeling from a second loss.