Harley Quinn's Revenge is the first story expansion for Batman: Arkham City, after several costume and challenge maps DLC packs released previously, and it takes place after the events of the original game with a campaign of about two hours. Batman has gone missing and Harley Quinn has taken over the Joker's former base of operations and his gang. The game opens with the player controlling Robin as he investigates where Batman has gone. After that first part there is a flashback to two days before Robin's appearance to show what happened to Batman. In those parts the player controls Batman as he investigates Harley Quinn's plans. The game then switches several times between the character's separate stories until the conclusion is reached.
Robin's moves and abilities such as the grappling to zip kick an opponent's chest, throwing shuriken, or the bo staff that can be turned into a shield, are identical to those in the challenge missions of the Robin Bundle Pack DLC where the playable character was first introduced. The story is tied into linear progression and it does not feature the open world exploration or side quests of the original game. There is however a collectable set of Harley balloons to discover.