It's Oliver's last day at Slabside and he'll be released in six hours. On that same day, Diaz is being brought to Slabside to start his sentence. However, he paid off the guard who escorted him and in turn, he killed the other guards.
Stanley tells Oliver that he's going to miss him at the cafeteria and asks Oliver to get Laurel to help him with his appeal. Oliver says he won't help him because he killed Dunbar. Stanley claims he was just doing what the Green Arrow always did. Oliver promises Stanley that he will rot in Slabside.
Oliver visits Turner in the pit and apologizes for believing Stanley. He promises to use Lyla's ARGUS connections to help him get out of Slabside because he can be a hero again.
Oliver gets a visitor, and it turns out to be Diaz. He tells Oliver he's going to kill him today but before that, he's going to make him suffer. And after he kills him, he's going to visit Felicity and William and kill them too. Oliver freaks out and is tased by the guards.
Diaz kills a guard and goes into the prison. Oliver warns a guard that Diaz is coming and will kill everyone in site. The guard doesn't believe him and even if Diaz is here, the guard believes they can handle it without Oliver's help.
Oliver creates a contraption in an ode to Shawshank Redemption and escapes his jail cell. He asks the guard one more time to let him take down Diaz but the guard refuses. He fights a bunch of guards off as he goes searching for Diaz.
Slabside is on lockdown while the guards look for Oliver. Diaz enters the backyard and gives a little pep talk to the inmates who are on their knees. He kills a bunch of guards before they can stop him.
Oliver runs into Sampson and Brick who have decided to side with Diaz. They engage in a brawl and Sampson and Brick get the upper hand after macing Oliver. Turner turns up and helps Oliver fight them off.
Oliver and Turner try to make a call for help but The Longbow Hunters helped Diaz jam the signals. Diaz has one of the guards as his hostage and forces him to say, "Oliver Queen, you have failed this city."
Diaz ends up killing the guard and wants Oliver to know that these men he's killing are dying because of Oliver. Diaz ends up releasing all of the inmates who attack the guards.
Oliver convinces Turner to help him save as many guards as they can. Turner escorts a few of the guards they saved to the panic room while Oliver goes and gets some weapons.
Oliver ends up getting injected with a sedative by Stanley. Oliver wakes up and has been tied up. He plays along and asks Stanley to help him and be his sidekick. An excited Stanley tells him where they can go to escape. However, Oliver refuses to leave all these people to die.
Stanley starts to go a little crazy, knowing that Oliver was willing to leave him to die because Oliver thinks he's a bad guy. He rants about killing Dunbar and other people outside of Slabside. Oliver is able to take him out and untie himself before locking him in a room.
Oliver meets up with Turner who escorted the guards to a safe space. Oliver doubts if he has the right mindset to stop Diaz, but Turner reminds him the old Green Arrow saw things in black and white, which is rarely the case. This new Green Arrow who sees the multiple shades of grey is the hero Slabside needs.
The inmates are torturing and beating up on the guards while Diaz watches from the video monitor. Oliver calls out Diaz and the two come face-to-face. Diaz hits Oliver with all the might his new found super strength can muster.
With Turner's help, Oliver takes out a bunch of inmates and frees the guards. Diaz ends up destroying the electrical system causing a fire to erupt. Turner escorts the inmates and guards who are still alive to the nearest exit while Oliver stays behind to take down Diaz once and for all.
Oliver and Diaz are alone in the Mess Hall. Oliver tries to fight him, but Diaz is just too strong now. He has Oliver beat in a cell, but before he takes him out, he tells Oliver that Felicity tried to kill him.
While he's distracted ripping up the photo of Felicity and William, Oliver manages to stab him in the stomach and headbutts him multiple times, rendering him nearly unconscious. He locks him up in the cell as the place continues to burn to ash.
Brick is at the morgue and is startled by Stanley. They both plan to escape through the morgue but before Brick can do that, Stanley stabs him multiple times before escaping.
Turner is one of the few inmates who survived and goes back to his cell. The guard thanks him for saving him and the rest of the guard's lives.
Meanwhile, Oliver is released from Slabside where Diggle and Felicity wait for him. Felicity and Oliver reunite with a passionate kiss.