Beneath the Surface

"Bruce, you've got a problem. Ever hear about Iron Heights, the prison airship? Yeah. Well, it just fell out of the sky. It crashed into Gotham Bay, You could have casualties or escapees."

- Nightwing informs Batman

Beneath the Surface is a Gotham's Most Wanted mission in Batman: Arkham Knight. The Season of Infamy DLC and 34% of City of Fear are required to unlock the mission. Killer Croc serves as the main villain with Warden Ranken acting as the story's surprise villain.

Plot
Nightwing has discovered that the Iron Heights Penitentiary airship has crashed landed in Gotham Bay and notifies Batman. Batman arrives to rescue any injured guards and prevent any prisoners from escaping. Batman enters the ship, only to find it destroyed, and in flames. Batman encounters Prison Officer Griscelli, whose leg has been broken. Griscelli tells Batman that Killer Croc has escaped his cell, and is leading a prison riot in an attempt to escape.

Batman then ventures out to save any remaining guards. He finds Prison Officer Burfitt trapped under rubble and saves him. Burfitt tells Batman that Warden Ranken is also trapped somewhere nearby. After Batman saves the warden, Killer Croc appears, slaps Batman with his newly grown tail, and kidnaps the warden. Batman tells Nightwing to head to his location. Nightwing arrives just in time to help Batman fight off many of the inmates.

After defeating the prisoners, Batman learns that Croc has taken the warden to the lower level of the ship. He finds the locked access door asks Prison Officer Blackburn how to open it. He is told that it is a two-man system that requires top security clearance. The only two men with such clearance parachuted out when the riot started. Batman tells Nightwing to go to GCPD Headquarters and put the prisoners in holding cells and get the guards to safety.

Batman contacts Alfred and asks for the location of the head guards. Then, he is given approximate locations and goes out to find one of the guards with the card. The first one had his necked snapped after landing on a crane and his parachute getting caught. Batman collects the key and informs Aaron Cash. He goes to the secondary location only to find Scarecrow Thugs attacking Prison Officer Riley, intent on killing him. Riley is reluctant to give Batman his security card calling Iron Heights a "complicated place". However, he relents and tells the Bat to forgive him because he was just doing his job.""The warden was experimenting on Croc and the other prisoners. Trying to weaponize his condition." "Looks like Croc wants payback. Can't say I blame him.""

- Batman sees a fate even Croc didn't deserve, while Nightwing understands the attack on the ship.

The Dark Knight heads back to the prison and Nightwing helps him insert the cards into the panel. While walking through the penitentiary, he sees a recording which reveals that the warden and other prison staff have been experimenting on Killer Croc and other prisoners in hopes of weaponizing Croc's healing factor. After watching the recording, both heroes realize that they have been helping the wrong people. They come across Croc interrogating Ranken about how to cure his mutation. Ranken insists that the process is irreversible. Batman attempts a surprise attack, but Croc's sense of smell detects the Bat. Batman and Nightwing fight both Jones and the prisoners. After fighting him, Batman interrogates the warden, and then knocks him out. After bringing both Croc and the warden back to the GCPD via the Batwing. Aaron Cash banters with his hated nemesis, while Officer Boulden escorts the warden to a cell in the West Wing Lockup. As a form of poetic justice, the warden is locked up with his prisoners and right next to Killer Croc.

Characters

 * Batman
 * Alfred Pennyworth (Voice and hologram only)
 * Nightwing
 * Killer Croc
 * Aaron Cash
 * Iron Heights Prisoners
 * Iron Heights Warden Ranken
 * Scarecrow Thugs
 * Prison Officer Griscelli
 * Prison Officer Burfitt
 * Prison Officer Riley
 * Prison Officer Blackburn

Achievements/Trophies

 * The Beast Beneath – Defeat The Prisoners
 * Breaking The Skin – Gain Access To The High Security Area
 * Evolution – Lockup Killer Croc In GCPD

Trivia

 * Killer Croc's fate in the DLC was foreshadowed in the Arkham Episode GCPD Lockdown, where his name is seen on a prisoner transfer list in the ending.
 * Depending on when you start the mission, Nightwing will look different if you don't complete the "Gun Runner" side mission his face will be intact but if you completed the side mission, Nightwing would have a bit of blood on his face and look a bit beaten up.
 * It is highly possible that the mission actually takes place before Gunrunner because Batman doesn't say goodbye to Nightwing yet. However, this is contradicted to the fact that Nightwing will have his gear he inherited from Batman after the Knightfall Protocol.
 * Although it's possible Nightwing had access to the tech and simply didn't use it during Gunrunner because he didn't need it.
 * Before the DLC's release, this mission was rumored to take place on a crashed Stagg airship with Red Hood, and would have been inaccessible until both City of Fear and Riddler's Revenge were completed. While this turned out to be false, the mission does take place on a crashed airship and Batman sides up with a former robin.