A Mexican drug cartel targets Danny when he intercepts a shipment of several million dollars; Jaime goes after a serial killer who preys on the elderly; Mayor Poole confides in Frank that he plans to retire.
When the skeletal remains of a young boy are discovered buried in a wall during a building renovation, Frank is determined to find the killer himself and close the case that began twenty-five years earlier when he was the detective in charge of the investigation into the boy's disappearance. As Danny and Jackie search for the person who murdered an escort, they uncover that the service for which she worked has a highly placed client subverting the cause of justice. Jamie has an unsettling encounter with Sonny Malevsky.
When the son of a Russian gangster is killed at his own engagement party, Danny delves into the world of the Russian mob and the family politics that exist. Meanwhile, Erin is thrown into a high-profile corruption case.
When an undercover counter-terrorism agent is shot, Frank assigns Danny to the case because he is the only officer he can trust given the victim's involvement with infiltrating a sleeper cell; however, Danny is sworn to secrecy as to not disrupt the police activity in that cell.
When a young girl is kidnapped and held for ransom, Danny and Jackie place her drug-addicted boyfriend at the top of their suspect list. Meanwhile, Erin and her boss, Charles Rossellini, take their flirtatious banter a step further.
When an unidentified young girl is found murdered at a debutante ball, Danny and Jackie look to the prostitute found giving her a hard time on the hotel's surveillance camera for clues. Meanwhile, Nicky gets a glimpse of her first murder victim as she rides along with Danny when he gets the call to investigate.
While investigating the murder of a homeless man, Danny takes a special interest in the case because the man is a decorated Marine. Eventually he learns that three wealthy men were the ones who killed him. While he gets one of them to admit to what happened. The other is protecting the other one who was the one who had no remorse about killing him. When the man is released due to lack of evidence, Danny places his career on the line to get him. And Frank learns that someone leaked to the press he is considering running for Mayor which he is not.
Danny witnesses a murder. He identifies the man and learns that he is the leader of a deadly gang. When the man is arrested he warns Danny the risks of testifying against him, Danny ignores him. But when Linda who's suppose take into protective custody is taken by gang, Danny tries to find her before he has to testify.
After his car, inherited from Joe, was sabotaged and damaged in a crash, Jamie tells his father and Danny about the Blue Templar spy status he 'inherited' unwillingly. Grandpa chips in to sketch how the secret society started to clean up NYPD from within where IA failed, but soon started turning bad with new blood. Together, they trace suspect cops like detective Sonny Malevsky and a dirty IA inspector to the present generation, which will stop at nothing to cover up its lucrative crimes, and can't be officially handled.
When a supporter for the mayor elect is found dead, Frank is put on the spot when the mayor wants him to position it to the public as a random act of violence. Meanwhile, Jamie goes undercover at a bar and meets a suspicious patron.
Erin reopens an 18-year-old rape case, in which Frank was the arresting officer. Meanwhile, Danny and Jackie investigate the murder of three teenagers in a park, who seemed to have been killed for no reason.
Grandpa Henry is approached by a fellow ex-NYPD-officer to consider the joining security firm Ajax Corporation, which is after police outsourcing contracts. To catch a serial 'escort' killer, Danny grudgingly guards partner Jackie, who insists on volunteering as bait since she physically resembles all victims.
Ayla Demir falls to her death within Jamie's reach. Her hot-tempered boyfriend Kyle Freelander's only alibi are his visiting parents. Her brother Hafiz firmly denies any suggestion of a honor crime as barbaric. Jamie discretely seeks help for his mentor's loan-shark problem. Henry Reagan's heart attack during Thanksgiving preparations ultimately only shifts the family spirit to hospital. Undercover FBI agent Anthony Deleon asks Erin's help against suitor Jacob Krystal, whom Interpol suspects for years of art robberies, for which he invokes an illegal excuse.
Danny accompanies a dangerous ex-mobster who is helping him find bodies on cold cases in exchange for leniency for his son on grand theft auto. Meanwhile, Jamie works undercover in a boiler room operation, looking for a secret about the Sanfino family.