"No Man's Land" part 31 and "The Code" part 1! Harley returns just as the Joker expands his turf over the broken bodies of two warring gangs. While she uses a philosophy called "The Code" to try to manipulate events to her liking, Joker makes a sweeping move that threatens to tip the balance of power. Continued in DETECTIVE COMICS (1937-2011) #737.
The Code Part 1: Breaking The Law
Joker and Harley Quinn take over and loot an abandoned and fully furnished apartment building. Harley moves into an empty apartment and flirts with a new henchmen to try and make the Joker jealous and take their relationship seriously.
In order to set his turf apart from the others the Joker decided to hold an election against a pig - Detective Petit.