Batman: Arkham Origins Blackgate is a completely separate experience that takes place after the events of Arkham Origins inside Blackgate Penitentiary.

 

Three months had passed since the events at Blackgate, and Batman had effectively become feared among the criminals. However, several criminals were also challenging Batman, forcing him to keep himself one step ahead. One night in Gotham City, he witnessed a catburglar named Catwoman breaking out of a building with stolen data, and confronted her.

 

However, he was forced to deal with both Catwoman and the Omega Squad of the Department of Extranormal Operations who were also after the data, the latter group under the belief that Batman was an ally of her. Upon cornering her at a construction site and defeating her, he learned that Catwoman had already managed to upload the data she stole to her employer, and even she doesn’t know what the data was. He then left her to the GCPD who had the area surrounded.