Shortly after Batman captures the Joker once again, sending him to Arkham Asylum, Joker is met by the Dollmaker in his cell. Joker seemed to have been expecting him, allowing the Dollmaker to slice off his face, then helping him escape from the asylum, leaving the face behind as a sign that he is once again changing. The GCPD take the face, and store it in their building, but with no sign from the Joker, who has presumably gone into hiding, his followers start constructing monuments to him outside the GCPD building in a bizarre ritualistic fashion.
Later, Harley Quinn breaks out of jail and heads for Gotham where she intends to find Joker's remains. She manages to get hold of the face and places it on her former Suicide Squad teammate Deadshot in a bizarre ritual. She speaks to Deadshot as if he is the Joker, a game which he plays along with to distract her long enough so he can shoot her, thus completing his mission.
Then, in the GCPD evidence room, Harvey Bullock tells a new rookie cop a creepy story about one of Joker's cop-kills. He then leaves her to stay in the room at night with the recovered face, as it's her job. Late at night, the face begins to laugh eerily. At first, the rookie thinks she is just imagining things, but it laughs louder and she decides to take it out of the case to reassure herself. At that moment, it laughs loudly, and she throws it in fear, but then realizes an audio player is taped to the back of it. It was all, in fact, a prank by Bullock to initiate her into the police force.
Across the street, in an abandoned building, a figure looks over the GCPD building from the shadows and says to himself, "Time to put on a happy face!"