Danny considers retiring until Erin asks for his help with a case involving her ex-husband; Jamie and Eddie pose as a couple; Frank clashes with the new mayor.
Frank is ordered to attend a parade honoring a man who conspired in a bombing against the police; Danny investigates the return of a teen who suspiciously disappeared 13 years ago; Jamie and Eddie try to help a woman they believe is being exploited.
Erin's trial against a human trafficker is jeopardized when the presiding judge is found dead; Mayor Dutton opposes Frank's public safety initiative, but a plan is devised to bypass the mayor's veto.
Danny and Baez investigate a case of a detective who was gunned down prior to testifying against a career criminal; Frank personally investigates when Garrett is attacked by a SWAT team outside his home; Erin brings in a confidential informant.
Danny and Baez investigate the murder of a single mother whose ex-husband has a history of violence; Mayor Dutton eliminates solitary confinement in prisons; Jamie's efforts to save a young woman who overdosed on drugs has unexpected consequences.
A famous basketball player is found dead of an apparent drug overdose; Danny looks into possible ties to a local drug gang; Erin revisits the case of a man she may have wrongfully convicted years ago; Frank is approached by Archbishop Kearns.
A case turns personal when Danny works to protect a nurse from her violent ex-boyfriend; an acquaintance of Frank's comes forth with a theory regarding the death of an inmate; Jamie and Eddie help deliver a baby.
Eddie's judgment is clouded by her past when she arrests a loathed college acquaintance; Frank is hesitant to mar the spotless record of a member of the force who tested positive for marijuana.
Danny and Baez join a narcotics task force to track a drug supplier; Baez comes into contact with drugs and gets an accidental overdose; Jamie and Eddie work to protect a rehabilitated sex offender; Frank forms an unlikely alliance with Mayor Dutton.
Jamie and Eddie ask Erin to drop old charges against a man who bravely rescued a woman from a local hostage situation; Danny and Baez work a case involving car thieves and discover the leader is a mobster they've dealt with before.
When a journalist disappears while working on an exposé about an innocent man serving time for murder, Danny and Baez hope that re-examining the original case will help them find her.
Anthony is shot while interviewing a witness; Erin enlists his archenemy, Danny, to investigate the case; Jamie and Eddie get in the middle of a standoff between a police lieutenant and a developmentally disabled man posing as an officer.
When Henry is the key witness on Danny and Baez's case, his meddling eventually leads them to valuable information; Nicky shocks her family by siding with her activist friend; Jamie and Eddie learn a parole officer is taking advantage of his power.
A student is shot by a rival gang member in his high school courtyard; Danny and Baez try to prevent further violence; the principal recklessly takes matters into his own hands; Erin tries to help a friend who is mixed up in an illegal gambling ring.
Danny considers taking a new, more profitable job after investigating the death of a wealthy man; Nicky tries to avoid involving her family when she is sexually harassed by her boss at her new internship.
A man living a double life with two separate families is murdered; Erin asks Anthony to help investigate his former partner; Frank deliberates between two candidates for the chief of transit position.
Danny forces his brother-in-law to help Baez take down the mobsters he's mixed up with; Frank suspects his old partner is guilty of a crime; Jamie is approached by an officer who wants help getting reassigned from his undercover assignment.
A woman voices outrage over her son's unsolved murder; Danny re-examines the case; Eddie gets shot while on duty; Erin and her ex-husband face off in court; Frank deals with an angry police force after the mayor fails to defend it.
Danny and Baez race to find a missing girl who will die without her heart medication; Jamie and Eddie are on the wrong side of an investigation after engaging in a car chase; Sean wins an essay contest.
Danny resorts to asking his incarcerated archenemy for help locating a dangerous criminal who escaped from prison; Lugo refuses to assist unless he's allowed to accompany them on the pursuit; Frank tries to convince Jamie to take the sergeant's test.
Frank locks horns with a data-tracking company when it refuses to unlock a terrorist's phone that may hold information regarding upcoming targets; Erin obtains information about an impending murder from a shady source; a woman kidnaps a baby.
When a series of drive-by murders occurs after six wrongly convicted men are released from prison, Danny and Baez wonder if the murders were orchestrated by the men as an act of revenge; Frank combats feelings of guilt.