After completing her college education as a young adult, Barbara Gordon had aspirations of following in her father's footsteps within law enforcement. However, her plans were thwarted by her father's over-protectiveness and societal biases against women in positions of power. This ultimately drives Barbara to embrace the vigilante identity of Batgirl.
In her journey, Barbara recounts the Greek myth of the prophet Cassandra, a tragic figure who concealed her identity behind a mask to hide her shame from those who dismissed her prophecies, even when they came to fruition. Her determination grows as she seeks her father's permission to join the Gotham City Police Department (GCPD), only to be met with refusal from her father, Captain James Gordon, who is worried about her safety. Seeking alternative paths, Barbara applies to become an FBI field agent, but her young age and small stature lead to her rejection, despite demonstrating exceptional capability.
Finding motivation in the costumes and bravery of vigilante heroes, especially Black Canary, Barbara sets her sights on becoming a formidable force for good. By hacking into her father's office and asking for assistance from her tech-savvy friends, Barbara is able to infiltrate the Justice Society of America’s headquarters, leaving behind a note requesting Black Canary to take her under her wing.
However, when she arrives at their meeting location in anticipation of meeting Black Canary, she is met by Wildcat, a member of the JSA. He expresses skepticism about Black Canary's interest in mentoring her and suggests that she give up. Disheartened, Barbara hears a cryptic prediction from Doctor Fate: "triumph and tragedy" awaits her journey.
In a state of despondency, Barbara withdraws for several days. Her father, seeking to cheer her up, invites her to an exclusive masquerade ball attended by the police and Gotham’s elite. Embracing her new alter-ego, she appears at the event sporting a modified Batman costume, humorously referencing her father's complicated relationship with vigilantes. Just as she prepares to make an impression, the party is disrupted by the novice villain Killer Moth, who attempts to abduct Bruce Wayne.
In the ensuing chaos, Captain Gordon is knocked out, and Barbara steps up to confront Killer Moth, allowing Wayne to escape and call in Batman and his sidekick Dick Grayson, otherwise known as Robin. During a tense encounter, Batman rebukes Barbara for donning his symbol. As the fight escalates, Killer Moth reappears in his helicopter, firing at Batman, Robin, and Batgirl, before ultimately retreating from the scene.
Back at home, Captain Gordon and Officer Jason Bard check in on Barbara, who feigns illness to explain her absence from the ball. Her father discreetly leaves behind a photo featuring Batgirl that raises Barbara's suspicions about whether he might suspect her secret life. Fueled by encouragement, Barbara fully embraces her identity as Batgirl, thwarting minor crimes in Gotham. She invests in new gadgets and attempts a daring stunt to test her rappelling gear, unaware that Batman and Robin are observing her from afar.
Meanwhile, Killer Moth, desperate to restore his reputation, approaches mobster Tony Bressi for help, only to be dismissed for having been outmatched by a girl. It’s revealed that Killer Moth is actually bankrupt ex-millionaire Cameron Von Cleer. Barbara's attempt at a daring leap from a building ends in a near-disaster when her rappelling rope snaps. Luckily, Robin swoops in to catch her, revealing that Batman had indeed sabotaged her rope for safety reasons. Frustrated, Barbara lashes out, only to find herself subdued by sleeping gas.
When she regains consciousness, Barbara discovers herself in the Batcave, where she impresses Robin during combat simulations. However, the encounter with Batman leaves her with disappointment as she struggles to articulate her motivation to join the fight, leading to her being knocked out once more. Following another awakening, Barbara finds herself back at home, anxious that Batman and Robin know her true identity.
Later, she receives a parcel from Robin containing high-quality crime-fighting equipment and a note expressing his faith in her skills. Meanwhile, Killer Moth, ridiculed and betrayed by his own, partners with the fire-loving Garfield Lynns, becoming Firefly. Together, they hatch a plot involving Captain Gordon, leading to violent chaos as they try to abduct him.
During her investigation into her father's kidnapping, Barbara encounters Black Canary, who wishes to assist in the rescue. With both determined to save Captain Gordon, they encounter the impending threat posed by Killer Moth and Firefly in a showdown that tempts fate in a greenhouse rigged to explode. Following a tumultuous battle, Barbara successfully saves her father while the villains flee.
Captain Gordon’s growing concern about Barbara's secret identity intensifies when he discovers incriminating evidence. Despite his worries, he is compelled to leave the situation as Batgirl once again dons her costume to confront the villainous duo. Displaying bravery, she pursues Killer Moth and Firefly, leading to a climactic encounter where she uses her skills to bring them down.
In an uplifting turn of events, Barbara receives an invitation from Batman to face simulations that challenge her abilities further. As these challenges unfold, Batman reveals his secret identity and the weight of responsibility that accompanies it. Barbara pledges to honor his ideals while seeking her place in Gotham's fight against crime.
Amid various challenges, Barbara continues to butt heads with her father as tensions simmer regarding her dual life. Ultimately, her determination in the face of adversity solidifies her role as Batgirl alongside Batman and Robin in Gotham's ongoing battles against its darkest threats, all while contemplating her future on this exhilarating path.