Batman (1940-) #570
"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.