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.

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.