On Christmas Eve, the serial killer Julian Gregory Day, also known as Calendar Man, faced execution for his mass murders, with Commissioner Gillian B. Loeb, who oversaw it. While he met a press release on the event, Loeb dismissed further questions after one of the reporters implied that it was actually Batman and not the GCPD who was actually responsible for Day's arrest.
Black Mask, however, after he tortured Warden Martin Joseph, and threatened his family, forced him to make security lax in order to engineer a prison riot inside Blackgate. After Black Mask and several of his henchmen, including Killer Croc, broke into the prison, a dispatch was issued that requested backup as Loeb and the news crew were taken hostage. Bruce Wayne, who overheard that dispatch, donned his identity of Batman and went to Blackgate to quell the riot.
Upon arrival, Batman deduced the entry point of Black Mask and his men due to the damaged entrance. After he saved Joseph from being brutally killed by one of Black Mask's Henchmen and defended himself from a panic-stricken Joseph, he then went further into the prison to locate Black Mask and Commissioner Loeb, as Joseph had no knowledge on either person's location. After he defeated several more of Black Mask's Henchmen near the cells and interrogated the last one about Black Mask's location, Batman continued onward, including defeating several criminals near the cell that the news crew was located. During his search, Batman also witnessed a drone flying around the prison. After he blew up a weak spot on the floor with Explosive Gel, Batman eventually located Loeb, Croc, and Black Mask, the latter of whom was in the middle of a speech that deplored the Commissioner for imprisoning several of his own men in the prison despite being on his payroll and demanded that they make "big changes" to the prison. After he subdued the prisoners, Batman then arrived at the Execution Chamber after he witnessed Croc savagely bite a prison guard. He then witnessed Black Mask release Calendar Man from the Gas Chamber and throw the hapless Loeb into it instead, under the pretense that Loeb was not part of his new plans. Batman was unable to save Loeb in time, but vowed that Black Mask had a lot to answer for before he defeated several more of Black Mask's Henchmen who arrived to investigate. While he escaped, Black Mask discovered the drone tailing him and ordered Croc to destroy it and take the memory card. However, Croc instead smashed it into the ground with enough force that caused a minor quake, and did not retrieve the memory card. An irate Black Mask then threatened to smash Croc's face if it turned out that his earlier action did not actually destroy the memory card as he claimed, which Batman overheard as he recovered the memory card.
Upon arriving on the roof, most of Black Mask's Henchmen escaped save for Croc, due to the latter smelling Batman, as well as several of Black Mask's men on standby. After Batman's arrival, Croc then fought Batman and tried to kill him, however, he ended up defeated. Batman then interrogated Croc about the whereabouts of his employer, only to learn that Black Mask had hired seven other assassins to attack Batman for a large reward. Batman then knocked Croc out and dragged him back to stable ground. Batman was then surrounded by the GCPD led by Captain James Gordon along with Harvey Bullock, although he managed to escape via the Batwing.
Because of Loeb's murder and the revelation of eight assassins (including Croc) in Gotham City, who aimed to collect the bounty on Batman's head, the city fell into chaos during Christmas Eve. In addition, when Black Mask, who was later revealed to be a new criminal mastermind known as the Joker, was incarcerated at Blackgate, another, far more destructive riot took place.