Damian, the new Robin, is still smarting from a rough night where he failed to stop the Joker, took a tumble from a building, and Batman had to pull him to safety, a moment captured by a video blogger and posted online. Alfred Pennyworth tries to reassure him that he is still learning, though Damian would prefer to talk to someone who has walked the Robin path, since Robin is away with his team.
In the Arctic, The Penguin has fallen into exile and feels the sting of loss. His only companions are Mr. Freeze and Buzz, a perceptive penguin who seems to understand Oswald’s predicament. Freeze tries to drive away a group of oil drillers near his ice cave, using one of his inventions to mutate an isopod into a gigantic monster to attack them, though the creature is ultimately defeated. The Penguin sees a way to capitalize on this, and urges Freeze to take him back to Gotham, promising a path to power for both of them.
Back in Gotham, Bruce Wayne and Damian attend a technology showcase at Wayne Tower, where Dr. Kirk Langstrom reveals a new drilling mech capable of melting rock to mine more efficiently. Bruce receives a call from Alfred that someone is attempting to break into Arkham Asylum. Green Arrow is present at the event and follows them as they depart.
At Arkham, the Penguin and Freeze drill into the asylum and free Bane, Chemo, Killer Croc and Clayface before escaping. At their undersea cave hideout, Freeze uses Bane’s Venom, Clayface’s protoplasm, and Chemo’s toxic waste to create a serum that mutates Killer Croc and Chemo into gigantic ice monsters who work together to freeze Gotham.
While on their way back to the city, Batman and Robin see the mutated monsters and attempt to intervene, but are unsuccessful. Freeze and Penguin turn on one another, each seeking control, while Buzz steals samples of Freeze’s formula. Bane and Clayface use those samples to transform themselves into even more formidable creatures. Despite his warnings about the serum’s effects, Freeze is easily defeated and the Penguin dispatches Bane and Clayface after Batman. The battle intensifies as Lava-Clayface poses a dangerous threat.
Batman hands the key to the Batmobile to Robin and instructs him to distract Lava-Clayface while a giant Bat-Mech is retrieved from Wayne Enterprises. [Green Arrow] arrives with a twist: Langstrom built an Arrow-Mech for him, after receiving a contract from Queen Industries for research and development. Batman then moves to confront Croc and Bane, while Green Arrow tackles Chemo. With Langstrom’s help, a plan is forged to turn the tide.
The Flash and Nightwing join the effort, lending their speed and agility to build a powerful laser cannon that can counter the mutated threats. Batman, aided by Green Arrow and the others, finally pulls the heroes’ plan together and presses forward to restore order. After a tense showdown, the monstrous foes are returned to their normal forms and the Penguin, along with Buzz, are captured by the Bat-Mech, while Freeze is taken into custody.
With the immediate threat contained, the Penguin and Freeze are arrested and sent back to Arkham, Buzz is placed in a zoo, and Langstrom begins to repair and upgrade the mechs for any future incidents. The other heroes depart the Batcave, and Batman extends his praise to [Robin], acknowledging how much Damian has grown more confident and capable. Yet the city’s shadows keep moving, as Clayface secretly escapes his ice prison and slips away into the sewers.
