Season Four premiere. The world of Oz--an experimental prison within a prison known as the Emerald City--reopens its doors with the inmates still on a 24-hour lockdown and prison officials struggling to end the hostilities.

The African-American inmates point the finger at McManus for letting Em City get out of hand. After that and his recent erratic behavior, McManus gets the ax from Glynn. Mobay's cover is almost blown.

Glynn learns from Adebisi that he was given the gun by former C.O. Hughes. Morales enlists Rebadow's help in taking Hernandez's place in the drug ring run by Adebisi and Pancamo. Mobay finds himself in a dangerous position.

Em City gets a new Unit Manager, Martin Querns, whose methods are hardly orthodox. Beecher's torment over his missing children is worsened when Schillinger presents him with an unexpected package. McManus returns to Oz in a new capacity.

As Querns implements his new course of action, the dynamics of Em City start to change, causing friction with Officer Murphy. Beecher falls deeper into depression as he wonders about the fate of his children.

In an effort to reduce violence, white inmates are transferred out of Em City. Said and Arif talk to Querns about the negative impact of his changes, but their efforts are in vain. Mobay gets in good with Adebisi's crew...but pays a price.

With things wild in Em City, O'Reily begins a surprising affair. Zabitz asks Schillinger for protection from Keller--who tries to get into the rehab program to make amends with Sister Pete. Beecher looks to get even with his children's kidnapper.

After Hughes' attack on Devlin, Glynn withdraws from the race. Miguel Alvarez is still on the loose. Supreme Allah receives an unwanted surprise. Hill pays big time when he tells Mobay he knows he's undercover. Meanwhile, Said does the unthinkable.

Six months have passed. Said was acquitted of Adebisi's murder on grounds of self-defense. "Up Your Ante," a game show, has joined Miss Sally in the prisoner's TV lineup. McManus and Glynn have done their best to keep the events leading up to Adebisi's death a secret. News producer Lisa Logan tours Oz in preparation for the arrival of hard-hitting reporter Jack Eldridge, who will also be spending a night with the new inmate the cameras will follow around on his first day. That man is Omar White, a jittery, homophobic addict fiending for drugs. Busmalis drives the cameras away. After an interview with Beecher Lisa considers focusing the piece on his struggles in Oz. Beecher taunts Keller and Ryan with on camera hints of their involvement in the murders; Keller threatens Ryan when Ryan wants to deal with Beecher; Pete dodges questions; Tidd interrupts a tense moment between Lisa and Vern. After a mention of Adebisi's drug-and-sex videotapes by Poet, Lisa decides to make the piece about the mystery surrounding his final days. Eldridge arrives, digging for information on Ryan after Ryan hints at their past connection. Eldridge blindsides Said with questions about his part in Adebisi's death. Worried about damage to Em City and his and Glynn's careers, Tim points Lisa toward the man he blames: Querns, who kept quiet in exchange for Glynn keeping quiet over his unethical methods. Per Glynn's advice, Querns turns down requests for an interview; per Querns' advice, Glynn destroys the tapes. Glynn and Jack have an off-the-record conversation, leading Eldridge to realize Glynn was a good man caught up in a situation he couldn't control. Jack cancels the Adebisi story. Offering him a constant supply of drugs, Ryan manipulates White into helping him settle an old score against Eldridge. Unfortunately, White tries to attack Eldridge directly in front of the guards. White goes to solitary. Eldridge chooses Cyril for his podmate, sensing good story potential. Cyril, who hasn't been taking his medication, remembers Eldridge and blames him for his mother getting cancer (Eldridge did a piece on Ryan on Cyril when they were in charge of their local Irish gang, painting them as monsters. Their mother developed and died from cancer not long afterward.). Cyril beats Eldridge to a pulp. As he recovers from serious injuries, the network decides to cancel the piece on Oz. Lisa resigns in protest.

New inmate Burr Reading arrives, ready to take charge of the African-American drug scene. Dr. Nathan returns to Em City, and finds the biggest adjustment is dealing with her feelings for O'Reily. Tidd tries to strike up a deal with Schillinger.

Morales looks to pit the Chinese against Redding. Alvarez offers Glynn his services as an informant as a way out of solitary. Dr. Nathan announces that Em City inmates will be selected to test a trial drug that could reduce their time behind bars.

O'Reily regrets getting Cyril involved with the trial drug when it starts taking effect. Meanwhile, Giles' request for an unusual execution creates controversy and the Chinese refugees are deported...but not before plotting revenge on Morales.

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 can't turn his back on White. Beecher tells the parents of the 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 secret.

In the Season Four finale, Hill discovers where his true allegiances lie in Oz. Redding's plot to use the Colonel against Morales has an unexpected outcome. Beecher's agony about his parole hearing leads to a shocking season climax.