In the last chapter of the walkthrough, you defeated Ra's Al Ghul and got a sample of his blood. It is time to go get the enzyme to Mister Freeze so that he can concot a cure! Oracle will contact you. She throught you were dead. But your readings are currently showing as normal so she thinks you are cured. However, Batman is currently alive due to the Blood of the Demon he drank during Ra's Trial. Report to here that Ra's and his forces are based underneath Arkham City, extracting some kind of naturally occuring chemical he's called "Lazarus". He's been using it for centuries, slowly perfecting the process until he  was even able to bring himself back from the dead. You will have to investigate Lazarus technology further when you are done there. You told Ra's to shut his pit down. Orale reports that in the meantime Robin gave her the blood sample, she patches you through to Gotham General. Robin reports that Gothan General has at least thirty confirmed cases, there are nearly fifty at Mercy and its looking like the pattern repeats all over the city. According to the Oracle's simulation Joker's Blood could be in as many as 2000 people by the morning. The first fatalities are expected soon after that. Hopefully the Blood sample you extracted from Ra's will complete the formula.

SOOOOOO Time to head back to GCPD. Your mission is to return to the GCPD lab to deliver the blood of Ra's Al Ghul to Mister Freeze. Retrace your steps to exit wonder city,  back through Wonder Avenue then through the collpased streets. Use line launcher to go through the gaps as before. Reach the sewers and subway. Penguin's guys have regrouped where the trains in the subway station are and you will have to defeat them. One of them has  a jammer again, locate the source of the jamming signal and dispose of that thug first. Keep making your way out. On the way to the surface. You will run onto an additional group og henchmen. They've started using shields They'll block head attacks, but that shield can't protect them from above. Adjust your tactics and perform aerial attacks on those thugs. Thugs using shields can stop most attacks. Use the Aerial Attack move to pound down on them from where their shield will not protect them. There will be yet another group of thugs towards the exit, this time a big group of 13 goons, some holding shields. Use the Aerial Attack to take out thugs using shields. Use Beat Down to take out thugs wearing Body Armor. Beat them and exit to the surface.

As you exit, Hugo Strange will announce that the Mayor, Quincy Sharp, has been arrested and is being brought into the facility. He was also the warden of Arkham Asylum. Hugo asks the inmates to give him the "welcome he deserves". That doesn't sound good. You will receive a new primary objective, to interrogate Quicy Sharp for information on Hugo Strange.

Quincy Sharp is not very from your exit point, so go ahead and find him. There will be thugs sprinkled over the area, dispose of those you have to or of all of them if you want more experience.

Defeat the goons that are guarding mayor Quincy Sharp. After that, find him laying on your ground and grapple him to to a roof. Politely ask him about the information you need. He will tell you about Strange and how he is tied into all of this. All the way back on how Strange came to him when he was a warden at the asylum and told him to turn a blind eye on his experiments and he would help him become Mayor. In return, all he had to do was set up Arkham City and put him in charge. You will have to find out who Strange is working with. But first, you must return to the G.C.P.D lab to deliver the blood and get the cure.