A fancy Gotham dinner gets crashed by a hoard of these "Eat to live!" zombie sort of people... are they really zombies? I don't really know... regardless, Batman shows up as well in an attempt to stop the attack, because that's what he does... Batman stuff. He then tries to radio Damian to find out where he is, but gets no response from his son, who is playing knocked out, in order to be lead to the base of these Saturn cultists.
While Bruce is trying to contact Damian, he has the batplane identify key components that he found in the blood of all the hoard members he defeated, giving him clues as to where they may be located. Meanwhile, as Damian is presented as a special meal to the cult, by the hooded leader. The cult soon fines out Damian has been playing them, as he wakes up, and takes on all who challenge him, as he attempts to lead an escape of all the other people kidnapped.
Damian leads all the civilians into an old train, where Batman eventually catches up to them, as the chemical analysis found traces of chemicals/elements/whatever that were only found in the old train system. Bruce isn't too happy, but first takes the time to help defeat all the cultists.
After the fight is over, Bruce again expresses his anger with Damian, claiming that it was reckless and irresponsible to turn off his communicator, especially when he was being played by the Joker. Damian doesn't believe it, claiming that Joker couldn't have been the leader, but sure enough, a chattering set of teeth are found on one of the near by bodies, with an image of someone's eye inside. (More on that later).
Back at the cave, Bruce brings himself to tell Damian he isn't sure that their partnership will work anymore, claiming Damian's lack of caring about anyone but himself would be the downfall. Damian then reveals what he's been doing alone in the sewers, which we've seen through out the months, and drops a single pearl on the table, telling his father that he does care. Shocked, Bruce picks up the pearl, looks at his son, and tells him how proud of him he is, as they hug.