The precinct squad rush to save Peralta and Santiago's wedding day from a major threat. Captain Holt gets an email revealing whether or not he has succeeded in his bid to become Police Commissioner.
Diaz and Santiago team up to take down a ruthless killer who has managed to elude them for seven years. Jeffords helps Peralta with his wedding chores. Captain Holt and his rival challenge each other.
The squad worry when Diaz responds to an active shooter alert, but they are told to remain at the precinct building and can't help her. Santiago and Gina try to repair the broken ladies' toilet.
Boyle organises an elaborate scavenger hunt for Peralta's bachelor party but the guys take short cuts that throw the event into disarray. Santiago's bachelorette party goes awry when a secret emerges.
When a fire destroys Boyle's food truck, Pimento unexpectedly shows up at the scene. Diaz helps Santiago to see it's fine to be excited about picking her wedding dress. Holt learns about social media.
Peralta invites his newly discovered half-sister Kate to come and stay with him in New York, but when he and Santiago realise she's a bit of a nightmare, they must find a way to get her home to Dallas
Peralta and Boyle realise they have been fooled into joining a cult-like pyramid scheme and struggle to terminate their contracts with it. Santiago feels the pressure on her first day as a sergeant.
Peralta and Santiago investigate a string of arson attacks that are connected to Santiago's favourite crossword puzzle author. Gina helps Holt to improve his Commissioner candidate presentation.
Peralta prepares for an all-night interrogation in the hope of securing a confession from a stubborn suspect. But when Holt sacrifices an evening at the opera to stay and help, the two officers clash.
Peralta is called on to negotiate a hostage situation with a jewel thief, only to discover the culprit is a familiar face. Santiago and Gina help Boyle with the demands of his new food truck business.
After mobster Seamus Murphy threatens Kevin, Holt devises an elaborate plan to hide his husband in a safe house, with Peralta as his guard. But Kevin and Peralta grow miserable with being cooped up.
Mobster Seamus Murphy returns to redeem the favour Holt owes him for helping to get Diaz and Peralta out of jail, so the team search for a loophole to get Holt off the hook without breaking the law
Diaz begs Peralta to help her break some big news to her parents, but her plan is thrown off track when Mr and Mrs Diaz jump to the wrong conclusion. Meanwhile, the squad have internet problems.
As the squad attend a funeral in Los Angeles, Holt hears he is in the running for his dream job: NYPD Commissioner. Santiago tries to prove she can be laid back. Boyle pries into Diaz's personal life.
Jeffords and Peralta ask Diaz to go undercover with them at a fantasy fiction convention to find the culprit who stole an author's manuscript. Holt, Santiago and Boyle take a forensics course.
Peralta and Santiago try to get their parents to bond over Thanksgiving dinner, but the family holiday doesn't go well. Captain Holt and Kevin's special Thanksgiving pie is stolen from Holt's office.
The Vulture makes an unwelcome return to Peralta and Santiago's lives. Boyle and Diaz must track down kidnapped NYPD horse Sergeant Peanut Butter. Holt challenges Jeffords to be less image-conscious.
To track down an arms dealer, Peralta and Jeffords go undercover at an illegal gambling club and Holt coaches them in the art of poker. Hitchcock and Scully have an unusual challenge for Diaz.
The precinct embarks on its fifth annual Halloween Heist. Everybody has a plan, no one is safe, and friendships are sorely tested in the contest to win the title Amazing Human Slash Genius by midnight
Officially back at the precinct, Peralta looks for a loophole to get out of his temporarily designated desk duty. Jeffords and Santiago support Diaz, who believes Pimento may be cheating on her.
Peralta is trapped by divided loyalties after the warden persuades him to investigate prison gang leader Romero's drug smuggling operation. A mobster offers Santiago information about Lt Hawkins.
Adjusting to life behind bars, Peralta bonds with his cellmate Caleb and is forced to join a prison gang led by notorious inmate Romero, while Diaz puts Holt and Jeffords to the test at visiting time