At an upscale restaurant in Gotham City, a crowd of members of the Saturn Club burst in, crying "eat to live!" Batman crashes down through a skylight in hopes of curbing their tendency to feed on living flesh. He shouts for the civilians to get down while he unloads a rapid fire of tranquilizer darts at the oncoming horde of apparently cannibalistic zombies. The tranquilizers are not strong enough, and he is attacked by two at once, causing all three of them to fly out the upper floor's window. Fortunately, he manages to catch them, and administer an even stronger dose of tranquilizer. He notes that they are certainly not undead, but they are very hungry.
Robin, meanwhile, is being carried by his own horde of cannibals through a series of underground tunnels. He follows the piping of the ceiling with his eyes, noting a steam release. He turns his head slightly, noticing an old steam-engine train nearby. He hears his father in his comm-link, but chooses not to answer, in order to protect the unconscious civilians with him from harm.
Batman, meanwhile, is analyzing a blood sample from the Saturnian, and discovers that it is a variant of the Joker Venom. This makes him all the more frustrated that Robin won't answer him. He has his computer isolate and identify a possible locality for the abnormal atmospheric variances found in the venom.
While the civilians are lined up, undressed, and washed in preparation for the Saturn Club's feeding, Robin is being kept aside as a unique delicacy. Naturally, Damian will not stand for that. Using explosives as a distraction, he urges those who still have control of their minds to follow him if they want to live. He shepherds them into a freight elevator, but it moves too slowly, and he is forced to cut the cable, and enter a free-fall. To save their lives, he blasts a hole through the floor and inflates a massive cushion to break the fall. Still not safe from the angry Saturnians, he ushers them onto the derelict train, aware that it will still work. He explains that it was once a secret transport for the president when he visited Gotham in the 30s.
As the Saturnians begin trying to break into the train's windows, even as it speeds down the rails, Robin assigns the controls to someone and then warns the horde that they will have to go through him before they get to the civilians he has under his protection. Fortunately, Batman appears to help, and the two of them battle the Saturnians until none remain standing, and the train reaches its last stop at Gotham Central Station.
Angrily, Batman explains that shutting off his comm-link prevented Damian from being warned about the fact that the Joker was behind all of this. A sound draws them to the pocket of an unconscious Saturnian, where Batman retrieves a set of Joker Teeth. Joker's voice comes from it, warning that something big is coming to swallow the pair of them. Rather than talk about it there, they return to the Batcave.
There, Batman explains that the blood sample he acquired helped him lock on to Damian's location, thanks to a rare concrete mix used in the construction of the secret tunnel. Damian tries to explain that he was only trying to protect civilians, but Bruce responds that he can't protect civilians by becoming a hostage himself. Damian is still only ten years old, and it's time he learned that his father knows more than he does.
Bruce explains that the reason he still keeps Jason Todd's costume on display in the cave is as a reminder to never let himself lose another son. He will not sit by and let Damian make choices that put his life in jeopardy. With that in mind, he is no longer sure that he can let his son share in the life he has chosen. After all, Bruce is terrified that Damian doesn't care about anybody but himself.
Damian promises that he does care, reaching into his pocket and retrieving a single pearl. Bruce picks it up, and realizes that it is one of the pearls from the necklace his mother wore on the day she was murdered. Damian had been combing the sewers in secret, trying to find it for him. Kneeling, Bruce takes his son in his arms, and tells him that he is proud of him.