Cassidy was a young pop star.
Cassidy was a famous rock star who was somewhat shallow, vain and demanding. By all accounts, Cassidy went through boyfriends fast, not committing to anyone. This pattern continued when she had a brief relationship with Garfield Lynns, who worked as a special effects engineer on her tour. She didn't show any sensitivity when she ended the relationship, and Garfield became violent and obsessed with her. She had hoped they could still work together as colleagues, but that was too much to ask from Lynns. Shortly before one concert, the two came to blows, and Cassidy fired him. Disgruntled, Lynns overcharged the show's fireworks, setting the stage on fire. As everyone fled, Cassidy was trapped on a dias on stage. Luckily for her, Batgirl swung her to safety.
Defiant, Cassidy refused to hide, even though she got another death threat. She went to the opening of Rock City, a club she had invested in. But Lynns still had his sights on her: he set the club on fire and confronted her, now calling himself Firefly. While Batman fought with Firefly, Batgirl brought Cassidy to safety.
Cassidy was shook up by the attacks. Her manager Frank did his best for her and had a strict security put up on her hotel room. Not strict enough for Batman, however: the Dark Knight slipped past security easily. Cassidy was disappointed he only came for information on Lynns: she would make his time worthwhile if he stayed with her for the night, but Batman refused.
Firefly did not attack during the night, but he did the next day. During a recording session, he put smoke bombs near the air conditioning units. While Frank and the technicians left, Firefly kidnapped Cassidy and brought her to Mephisto, an abandoned matchstick factory. He revealed his plans to her: to release a special flammable gel into the sewers. Upon ignition, all of Gotham would go up in flames and they would escape together.
Batman intervened, however, in the fight, the gel was ignited. Amid burning wreckage, Batman carried Cassidy out of the building. Firefly, wounded in the factory's collapse, was arrested.
As a result of the attention, Cassidy's stardom rose to new heights. Frank proposed cashing in on the fire-theme, but Cassidy was marked by the horrors she faced: she'd developed pyrophobia.