Things get a bit lively on death row after Shirley Bellinger's execution-- Miles begins painting a self-portrait, Ginzburg's health deteriorates from AIDS and Deyell severely injures himself. Mobay's ordered to kill someone as a final test of his loyalty and a new prisoner, whom Mobay's familiar with, makes the perfect victim. A call stirs McManus' emotions again. New inmate Supreme Allah arrives creating tension and uneasiness for Arif. On his way to his son's funeral, Beecher asks Keller an intimate question. A changed Rebadow asks for permission from Morales to kill again. After a fight with the gangsters, Cyril's put on heavier sedatives. For Ryan O'Reilly, he gets the cell phone after ratting to Hoyt and he also meets Dr. Nathan's attacker.

Ryan and Howell get frisky. After leaving the hole and apologizing to Busmalis for the stabbing Rebadow suffers an attack due to a brain tumor. Busmalis reacts by doing what he does best--start another tunnel. Unbeknownst to the doctors and everyone else, Cyril's recovering psychologically more than he can actually show. Arif confesses to Said about his own demons and asks for forgiveness and help. Said plots with McManus to end Querns' and Adebisi's control. Hank Schillinger beats the kidnapping rap and once Beecher finds out, he plots with Pancamo for revenge. After Keller reveals his plot to kill him, Eli Zabitz asks Schillinger for protection. Schillinger agrees but sends Robson to eliminate Zabitz instead. Hughes, now raging beyond sensibility, makes an attempt on Devlin's life at a press conference. Keller and Father Ray have an intense discussion about Beecher.

After Hughes's attack on Devlin, Glynn withdraws from the race. Alvarez is still on the loose. Supreme Allah gets an unwanted surprise.

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 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.

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.

Redding discovers that Busmalis lied about DeSantos. Furious, he confronts Morales and the confrontation gets the two of them thrown in the hole. Cyril gets convicted of the murder and Ryan tells the attorney not to appeal. Meanwhile Sister Pete, Father Meehan and Suzanne Fitzgerald meet to devise another plan in Cyril's defense. Rebadow fumes over not getting the lottery money. Mc Manus' offer to search Oz's databases reveals an inmate with the same blood history as Rebadow's grandson. Rebadow meets the man only to be rejected by him. The rumor of Robson's replacement gums coming from a black patient prompts Schillinger to consult with Aryan Nation leader. The result? Robson gets banned from the Aryans.

Glynn receives some good and bad news on the toxic-poisoning case. Meanwhile, Rebadow's relationship with Stella hits a snag; Keller and Beecher work out a mutually beneficial arrangement; Poet and Redding nearly come to blows; Hoyt is transferred from Death Row; and Robson finally gets some redemption.

Everyone has a different opinion of new inmate Idzik; Alvarez receives shocking news; Redding's attempts at reform continue; Murphy makes a confession to Glynn; Morales'(David Zayas) medical suspicions are confirmed; and Beecher's devotion to Keller leads him into a perilous position.

Idzik faces his enemies; the intrigues behind the Loewen case get more complicated; changes are made in the hospital; the Muslims run into business trouble; Rebadow and Stella get closer; and the inmates rally to support the O'Reilys.

Three new inmates arrive, one of whom is close to the O'Reilys; Busmalis and Rebadow prove to be "true Romeos"; the Keller-Beecher-Schillinger triangle gets more pointed; and an awards banquet ends in a fateful discovery.

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.