Selina Kyle stands trial for multiple counts of grand theft. The judge informs her that the penalty for her crimes is up to twenty-five years in prison. The fact that she committed her thefts to benefit animal rights causes is not a mitigating circumstance, but the fact that she helped Batman to save Gotham City from "annihilation" (the release of the viral plague stolen by Red Claw), she is handed a relatively lenient sentence of five years probation - a decision that receives heavy applause from Catwoman's fans in the gallery. However, the judge calls for silence and warns Selena that if Catwoman breaks the law again, she won’t be so lucky.
Bruce watches the news of Selina's sentencing. Alfred wonders why Bruce isn't more pleased, knowing how attracted Bruce was to her. Bruce says he's not convinced that Selina's reformed and decides to keep tabs on her. Besides, he adds, the idea of starting a relationship is dubious, since she is in love with Batman, not him.
Selina returns home in joy that she is free, but Maven sorrowfully tells her that Isis is missing. Maven accidentally left a window open and Isis escaped.
Determined to find her cat, Selina heads out to the fish market and asks about Isis but no one has seen her. Selina continues her search and finds a couple stray cats but Isis is still nowhere to be seen. Just then, a couple of thugs arrive and snatch the cats in a net. Selina confronts them over their kidnapping but they refuse to explain their actions and attack when Selina tries to stop them. Selina holds up her own against the thugs but they manage to gain an advantage over her and Batman is forced to step in. The two almost share a moment but the police arrive and Batman leaves. Unfortunately, the thugs claim that they were only trying to find new homes for the strays and that Selina attacked them. Selina denies it but Renee Montoya arrests her anyway.
Meanwhile, Roland Daggett watches as Dr. Milo injects a viral strain into a rather large dog that instantly becomes feral. Dr. Milo explains that the toxin acts almost instantly and just a nip will spread the disease. Daggett is pleased and tells Dr. Milo to complete his operation "by tomorrow night." Following orders, Dr. Milo takes Isis, whom had been captured, and injects her with the toxin. Selina is released from jail and discovers that Bruce has posted her bail. She thanks him for bailing her out but she only thinks of him as a friend. Bruce understands and warns her that the arrest could be bad for her. Selina is unconcerned and is more interested in why her assailants had an attorney from Daggett Industries working for them. Bruce warns her to keep away from Daggett and she assures him, "You won’t see Selina Kyle anywhere near Daggett Labs." She did fail, however, to say that Catwoman wouldn't be.
Suspicious of Daggett's motives, Bruce talks to Lucius about Daggett and learns that he's coming out with a new drug but no one really knows what it's for.
Believing that Daggett is up to something, Catwoman breaks into Daggett Labs and finds Isis. Concerned, she releases Isis but the virus takes hold and Isis bites her. The commotion attracts Dr. Milo and the thugs. Selina manages to escape but Isis runs away and the toxin starts to take effect. Catwoman becomes dizzy and clumsily chases after Isis but loses her and falls. Fortunately, Batman arrives and takes her to a hideout. Batman tends to Catwoman and learns about the bite and that something was done to Isis and several other animals. Elsewhere, Daggett complains that the operation is moving too slowly. Dr. Milo assures him that it'll be only a short while as he sent Paunch for the antitoxin in case of an accident. However, Batman reaches Paunch first and interrogates him for information about Daggett's plans. Batman manages to figure out that Daggett is planning to infect stray dogs and cats with a virus, which will blanket the city in a matter of weeks, then make a fortune selling the antidote. Unfortunately, Daggett and his henchwoman arrive and she fires on him with a machine gun. Batman manages to elude the gunfire but Dr. Milo releases an infected dog, which chases after him.
While the dog chases Batman, Daggett sends his thugs after him to make sure the job is finished. For a time, Batman manages to elude the dog and runs for Selina's hideout but the dog and the thugs catch up with him on a frozen lake. Making matters worse, the ice is thin and Batman can't run. The dog manages to catch up with him but Batman sprays it with a dose of the antitoxin causing it to calm down. Though the dog has stopped attacking, the thugs shoot at him, causing the ice to break. Batman and the dog fall into the water but only the dog emerges. Batman is okay, however, and grabs onto the thug’s legs from under the ice. Frightened, they shoot the ice and fall in themselves. Batman then captures the thugs and cures Catwoman.
Returning home, Selina discovers that she's now considered a hero, but without Isis, the victory seems empty. While she mourns the loss of Isis, a basket, holding Isis drops down. Isis happily jumps into Selina’s arms and both pet and owner are re-united.