It's your typical night in Gotham, pile of dead corpses and fish, you know, the usual. Bruce and Damian are on the scene, looking for clues, which are hard to find in a literal pile of bodies. Bruce eventually finds something, a fish with the Joker's face on it, but as he soon comes to find, it was a bomb, and that bomb goes off. Damian wakes up shortly after, and digging through the mess, he eventually finds his father, dead.
After burying his father, a grief stricken Damian seeks help in the most unlikely of places... from his mother and grandfather. Knowing full well what they're answer will be when he asks them to help find out who killed his father, Damian isn't surprised by Talia and Ra's' answer of "no." But what does surprise Damian, is his grandfather telling him it is his time to become Batman, which Damian hardly acknowledges.
Back in Gotham, every major villain is claiming that they killed Batman, and Damian, one to seek revenge, decides to hunt each one of them down, in his own brand of violent justice (remember what happened to the spook? Yeeeeeah). Mr. Freeze, Killer Croc, Jackanapes, all fall to Damian's hand.
Some time later after his bloody crusade has begun, Damian seeks guidance in a church confessional. The priest, who Bruce had seemingly sought guidance from (under the guise of Batman), tells Damian that his father would be disappointed in him. This angers Damian, and he storms off, defending his more permanent methods, claiming the priest doesn't know him. As the priest watches him leave, he says to himself "But I do, Damian. I do..."
Back in the manor, Alfred is reading of mysterious murders befalling villains, all but tells Damian he knows its him, once again reminding him how his father would disapprove. Damian lashes out at Alfred, blaming himself for his father's death, and claiming he's handling it in his own way. As Damian suits up to go out for the night, a stern voice yells at him to stop, and holy shit, look who it is... fucking Bruce Wayne.