See chapter 1.
He and Batgirl had received an invitation. They had gone to the rooftop specified and she had never seen him so angry as the moment when he figured out that Robin was being kept in Arkham. Batgirl went with him. She had already decided that if things got ugly or out of hand she would be there to protect whoever kidnapped Robin from Batman.
The old Arkham asylum looked empty. They searched the entire building and they found Harley stabbed to death on the floor. At first Batgirl thought that The Joker had finally snapped but she found him in a puddle of water with live wires still dancing around his lifeless body.
Batman exited the old Operating Theatre. There had been a video playing on a continuous loop. It was The Joker torturing Robin over and over; Robin in the corner unmasked, shaking from all the 'shock treatments' and babbling everything that he could figure that the man would want to know. Batman just shook his head; he couldn't imagine everything Tim had gone through. He was sure that the boy was still alive. He saw Batgirl in the hall. "Did you find them?"
"Them? The Joker and Harley are dead. I haven't found Robin."
Batman scanned the small hallway. Robin was trained very well; it would've taken a long time before his mind cracked. If he did lose hope and just give in to whatever The Joker had planned for him, he was sure that Robin would have left him some sort of clue. He started walking down the long hallway. Batgirl knew that he'd handle this badly but she never imagined that he'd be this silent, brooding and probably looking for a body. He turned the corner that lead into a different room. She followed carefully and tried not to gasp at what she saw.
The room was no bigger than a prison cell. There was a mattress on the floor and in the corner there was a hole cut into the floor. The walls were covered in scratches. Some were written pleas for help. Then the writing would get shaky and some would just be HAHAHAHA. Then all over the floor was the same thing over and over.
DADDY LOVES ME
Batman had moved to where the mattress was. It took him a minute, but then she realized what he was looking at, bunched in-between the edge of the mattress and the wall was Robin's mask, utility belt and his "R" shaped throwing disks. Batman picked these things up and walked away. As they left the building Batman was more resolved then ever to find Robin. He was convinced that his partner was still alive. He just didn't know where to look.