A female gardener digs up a flower and then stands to watch a crowd some distance away. Mayor Hamilton Hill, Harvey Dent, Bruce Wayne, and Commissioner Gordan have gathered before the press out in a field, where they are planning to build the new Gotham Penitentiary facility. The facility is naturally funded by Wayne Enterprises, and is the brain child of Harvey Dent, Gothams new District Attorney. As Dent breaks ground over the building site, he promises that this institution will build a better, safer Gotham. That night, the gardener rips the article out of the newspaper and posts it above the flower she rescued from the field.
Five years pass, and while the facility has been built, we quickly see Dents promise of a better, safer Gotham hasnt arrived yet. A helicopter swoops into the prison yard as alarms sound. A convict leaps into the helicopter and it soars away. Gordon receives the call and scrambles his police force into action. Even though the police are after him, the prisoner believes that hes home free. However, theres one thing he hasnt taken into account: Batman. The Dark Knight watches the helicopter pass by him, and then latches his grappling hoot onto the wheel strut.
While the frantic chase takes place high above them, Harvey Dent is dining with his new acquaintance, the gorgeous Pamela Isley, at the Rose Cafe. Theyve been waiting for Bruce, but Harvey says they should go ahead and eat. After all, Bruce probably got held up on business. Meanwhile, Batman manages to loop his grappling hook wire around a radio antenna and brings the helicopter crashing down onto a rooftop. Dent informs Isley that Bruce runs around with a high-class crowd as Batman chases the escaped convict across the rooftop. While Dent is confident that theres nothing we dont know about each other, Batman snags the convict and turns him over to the police. Bruce finally arrives at the Rose Cafe to conclude the evening with Dent and Isley. Pamela suddenly realizes that she has to leave and gives Dent a passionate kiss before taking off. Once she leaves, Dent confides to Bruce that hes asked Pamela to marry him. Bruce is stunned, since Dent only met Pamela last week. Harvey tries to explain to Bruce how much he loves Isley, but he seems a little flustered. Suddenly, he collapses face down into a plate of chocolate mousse.
Dent is rushed to the hospital and taken to intensive care. Gordon receives the call and once again scrambles his police force to meet at the hospital. The doctor finishes his diagnoses and tells Gordon that Dent has been poisoned. Gordon sends Bullock down to the Rose Caf to get some answers. Bruce meets with the doctor, who is studying a blood sample from Dent, and finds out that its not a case of simple food poisoning, but rather a virulent strain that is racing through Harveys system. If Harvey doesnt receive an antidote soon, he could die. When the doctor leaves the room, Bruce swipes the blood culture.
Back at the Batcave, Batman has isolated the toxin. Its a lethal poison derived from the plant Rosaceae vularis, the wild thorny rose which has been extinct for nearly five years. Batman believes that this means theres no antidote. Bruce returns to the hospital, just as Pamela arrives. She tries to get in to see Dent, but Commissioner Gordon has ordered that he can't receive any visitors. Isley is distraught, so Bruce offers to walk her out to her car. At the car, Isley thanks Bruce for being such a good friend to Harvey and tries to kiss him, but Bruce just hugs her. As he does, he recalls the passionate kiss Isley gave to Harvey shortly before he fainted. Batman finally has a lead.
When he arrives back at the Batcave, Alfred has managed to dig up some information on Pamela Isley. Apparently, she is a research chemist who works at developing new fragrances, the newest of which is called Nightshade. She also conducts lectures on endangered and extinct plant species. Batman rides out to Chez Gerard to confront Isley. Gazing inside the greenhouse, he spots Pamela tending to the wild thorny rose. Once she leaves the room, Batman leaps down and races towards the plant. However, he steps through a trapdoor and almost falls to his doom, this time of the spiky plant variety. He grabs hold of a rope-like object and clambers back to the main floor. However, the rope is a tendril from a massive flytrap, and Batman is quickly wrapped up and dragged towards the creatures mouth. While Batman tries to fend off the flytrap, a new villainess approaches from behind: Poison Ivy. Ivy explains to Batman that Dent had to pay for his crime, namely killing all the wild thorny rose bushes to build the penitentiary. She then kisses Batman, giving him a healthy dosage of her rose poison. She then has him smell the antidote. Taking advantage of her closeness, Batman knocks her backward and then cuts himself free of the flytrap. Batman is still disoriented, and barely manages to dodge a dart from Ivys wrist crossbow. The dart rips through his cape and through the flytrap. The flytrap begins to scream out its death wails, and Batman has to run as Ivy launches more darts at him. Batman ducks into the foliage and then tries to launch himself up into the ceiling. Instead, he wraps his grappling hook around a flood lamp, and his weight pulls it from its ceiling mount. The light falls into a pool of water and starts a fire. Ivy tries to save the rose, but is surrounded by falling debris. Batman knocks her out of the way as a flaming tree drops towards her, and winds up dangling over the trapdoor. Ivy prepares to kill him, but Batman reveals that hes holding the rose bush. He exchanges the rose for the antidote, and then helps Ivy escape the greenhouse.
Dent recovers from the poisoning, and Bruce tells him that he should rethink his engagement to Pamela. At Arkham Asylum, Pamela swears vengeance on Batman. They can bury me in the ground as deep as they like, she tells the wild thorny rose, but Ill grow back. We always grow back.