Brigid O’Reilly is a true-blue detective, believing in the letter of the law and arresting those who take it into their own hands - in other words, vigilantes. When corrupt cops leave her for dead from toxic gas inhalation, her whole world changes and she is reborn as Mayhem, a super powered mutate that can control venomous gas. Unable to go back to who she once was, O'Reilly then becomes one of the vigilantes whom she herself had previously hunted down.
Brigid O’Reilly becomes a detective in New York City and while investigating the mysterious vigilante duo Cloak and Dagger, she tracks them down to a gunfight, where a young man is struck by a stray bullet and killed. O’Reilly blames them for his death claiming she could have saved him if they hadn’t interfered. She makes it her mission to protect innocents against private citizens engaged in vigilantism.
Venomous Gas and Flight
As a detective, O’Reilly has excellent perception and investigative skills. She is also trained in the typical hand-to-hand combat that police officers receive and has expert marksmanship with her service revolver.
After she becomes Mayhem, she is able to surround herself with a venomous gas that has a paralyzing effect and can act as a truth serum. Mayhem’s hands were also affected by her rebirth in that she now has talon-like fingernails. She uses her nails against others so that her gas can enter their bloodstream more quickly.
Her abilities to control gas also grant her the power of flight in that she can use the gas to levitate herself.
Corruption on the Force
Roger Falcone, a corrupt police officer, exposes O’Reilly to a deadly gas that kills her. However this activates her mutant superpowers, allowing her to return to the world as Mayhem, swearing vengeance upon the man who caused her death.
Vigilante Allies and Family Ties
Cloak and Dagger while an initial threat to Mayhem when she was a by-the-rulebook detective, after becoming a vigilante herself, she becomes their ally and fights corrupt police officers alongside them.
When Brigid becomes Mayhem, she leaves behind her favorite uncle, Father Michael Bowen and her partner, Detective “Rusty” Nales.
Record of a Detective-Turned-Vigilante
Cloak and Dagger depart from the gunfight before O’Reilly could arrest them, but their temporary escape did not stop her from bringing them to justice. O’Reilly suspects that local priest Father Delgado aides them so she confronts him. While he denies the connection, she stakes out his church and sees him later leave with a wounded Dagger.
O’Reilly hides out in the church’s confessional and waits for Cloak to apprehend him, but robbers take an opportunity to strike. Cloak appears and a battle ensues with O’Reilly stuck in the confessional. When she makes her way out, she attempts to arrest Cloak but he produces the psycho killer Duane Hellman from his cloak giving O’Reilly no reason to arrest him. She eventually learns to trust the vigilantes and works with them.
When O’Reilly gets a tip from corrupt policeman Roger Falcone about a millions of dollars’ worth of dope stored in a warehouse, she leads a squad of police officers to it, though suspects disloyalty on her team. They arrive to the warehouse and find a chemical lab filled with pharmaceuticals from the same company that gave Cloak and Dagger their powers. When some of O’Reilly’s team turns on her and other cops, they are led by Roger Falcone who exposes them to a deadly gas.
The gas killed Brigid but before she died, she swears vengeance on Falcone. Cloak and Dagger do their best to save her but it appears that she dies and they leave her apparent lifeless body behind. Brigid is then reborn mutated as the superpowered Mayhem.
After O’Reilly is reborn as the mutated Mayhem with control over venomous gas that is emitted from her pores, she becomes a vigilante herself, swearing vengeance upon Falcone who killed her. She follows through with this threat and kills Falcone.
She later tried to atone for her merciless deeds and comforts a blind Dagger with her lessons learned.