An investigation into Goergen's death starts and Mobay's anxious when the investigator targets him first. Tensions begin to rise as Querns turns a seemingly deaf ear and blind eye to the blatant violations committed by black inmates. An inmate transfer works in Adebisi's favor. Arif challenges Querns's authority. Ginzburg's poor health forces him to request an early execution and Sister Pete convinces Glynn to make it happen. Glynn's press conference announcement forces his daughter to make a major decision. Beecher's daughter arrives alive and Keller confesses to Mukada.

New inmate Burr Redding arrives and stands ready to assume control of the drug business. Dr. Nathan returns. Tidd approaches Schillinger with a plan to kill Said. Several Asian refugees are housed in Em City while the government decides their fate and they unwillingly get caught in a power struggle between Morales and Redding. Glynn hires an energetic new assistant who piques everyone's interest.

Robson and Hoyt tell Rev. Cloutier to back off of Schillinger. Schillinger and Beecher have their first counseling interaction session. Tidd continues to get close to Said by defending Arif in a fight. Arif goes to Said and pleads Tidd's case to accept him into their Muslim group. Busmalis requests that he and his girlfriend be married. Glynn hosts the Warden's conference and is given an update on Hughes by Querns. Glynn soon has Hughes transferred to Oz's cops unit so he can protect him. This unit is also where Johnny Basil (Mobay) is locked up. Keller's old buddy Ronnie gets close to Beecher causing Keller to get jealous. Ronnie's offered a sentence reduction in exchange for corroborating evidence of Keller's involvement in some past murders. Beecher finds this out and warns Keller, who doesn't believe him. Keller question's Ronnie about the matter and then, comes up with his own solution. Em City inmates are selected for drug testing experiment that promises to age the person quickly therefore reducing their actual time spent in prison.

O'Reily is in for a surprise when a visitor reveals the truth about his past, while Cyril faces trouble for his difficult behavior. Meanwhile, Morales and Redding lay out plans that could lead to all-out war in Em City.

McManus calls a superficial truce between Redding and Morales. Basil finally sees his wife, but Hughes ends up spoiling their happiness. Meanwhile, Cyril's latest outburst proves to be the last straw.

McManus finds he is unable to turn his back on White. Beecher tells the parents of the young girl he killed that he's up for parole. Howell tries to blackmail O'Reily so she can get to Cyril, but he throws her for a loop--and then O'Reily is thrown himself by a family secret.

In the Season Four finale, Hill discovers where his true allegiances lie. Redding's plot to use the Colonel against Morales has an unexpected outcome. Cloutier runs into trouble from his church on the outside and his parishioners in Oz. White gets a little too close to McManus. Beecher's agony about his parole hearing leads to a shocking climax.

A ribbon cutting ceremony, complete with the Governor doing the honors, signals the opening of a newly constructed Oz. Warden Glynn doesn't resign but he's more battle weary. White, Alvarez and other inmates in solitary are temporarily transferred to Em City while repairs are being made. As Schillinger and Robson recover from their wounds, they begin planning revenge on the Muslims. Conversely, Said plans to plead guilty for the attempted murder of Robson & Schillinger. The fate of Rev. Cloutier is revealed and inmates expecting visits from family members get shocking news.

Alvarez and Guerra come up with a new way to settle their beef -- Guerra will stab Alvarez in the shoulder without killing him. Morales questions Guerra's decision to do this while he attempts to grieve for his sister. Rebadow gets more bad news about his grandson which prompts him to search for alternatives. Montgomery asks for more hush money from Ryan so Ryan devises a plan to have Montgomery eliminated. Officer Brass returns to Oz to get facts on who attacked him. Ellie O'Connor arrives as the Governor's liaison to Oz only past memories of her failed marriage to McManus return. Schibetta returns and Schillinger shanks Pancamo after learning that he had Hank killed. McManus makes an offer to Said and White to hopefully curb White's erratic and sometimes bizarre behavior. Ryan's mom, Suzanne Fitzgerald comes to Oz to instruct inmates in performance arts.

Guerra kills Alvarez's new follower and the guilt surrounding it forces Alvarez to make a confession to Mukada. Alvarez, Hill and Penders sign up for a seeing-eye dog-training program. Dr. Nathan attacks a patient while having a flashback of her rape. Cyril shanks and kills Li Chien, which gets Cyril sent to solitary and Ryan sent to the cage. During an interaction session Beecher attacks Schillinger after Schillinger denies ever raping him. Redding asks Glynn for control of the kitchen. Hill's grief over his dead mother and divorce from his wife send him back to drugs happily supplied by Poet. Beecher's new podmate is the son of a prominent family Beecher knew well. Because of that, Beecher decides to protect him from the Aryans at all costs.

The unexpected arrival of Mayor Wilson Loewen at Oz spurs an ironic turn involving Schillinger and Beecher. Meanwhile, Dr. Nathan discovers why solitary inmates are getting sick; a new business plan within Oz inspires Redding; Schibetta looks to puts a curse on the O'Reily family; and some Death Row prisoners get a bang out of a magazine photo shoot.

Oz is in upheaval following the return of Martin Querns. Meanwhile, Howell and Robson each receive troubling news, Mukada answers an unsolved mystery, and the O'Reilys struggle to make amends. Finally, the prison production of 'Macbeth' ends with a staggering final act.