This book is about the efforts of Batman, district attorney Harvey Dent, and Gotham City Chief of Police Jim Gordon to take down the mafia boss Carmine "The Roman" Falcone. As the story progresses, a mysterious serial killer referred to as Holiday begins killing members of Falcone's family and gang. In the end, the pursuit of Falcone drives Dent to break the law and transform himself into the villain Two-Face.

The book opens at a wedding party for Falcone's nephew Johnny Viti. Bruce Wayne attends the party to tell Falcone he will not allow Falcone's money into Gotham City Bank. Batman makes a pact with Dent and Gordon to catch Falcone but not break the law in the process. On Halloween, someone murders Viti in his bathtub, and Batman and Dent burn down a warehouse full of Falcone's money. When Dent returns home, a bomb goes off in his house.

Batman and Gordon question the gang responsible for bombing Dent but cannot get them to tell who paid them to plant the bomb. The gang is released and makes bail quickly. As they celebrate their release with a Thanksgiving dinner, the entire gang is murdered in the same way Viti was.

The Joker escapes from Arkham Asylum near Christmas and accuses Falcone's chief rival Salvatore Maroni of being Holiday. Maroni denies it, so the Joker moves on to Dent's house and accuses Dent of being Holiday. The Joker finally proceeds to Falcone's penthouse, where he tells Falcone to find Holiday or the Joker will kill everyone in Gotham City. As the Joker flees the penthouse, Holiday kills Falcone's main bodyguard, Milos.

On New Years' Eve, the Joker steals a plane to drop poisonous laughing gas on revelers in Gotham Square, but Batman stops him. At the same time, Falcone's son Alberto is shot by Holiday.

On Valentine's Day, Dent and Gordon go looking for Wayne regarding a connection to Falcone at Wayne Manor, but Wayne is out as Batman confronting Falcone. Holiday kills a number of Maroni's men with a car bomb. Wayne is pricked by a rose given to him by Poison Ivy and falls under her control.

Under Poison Ivy's control, Wayne approves Falcone's money for Gotham City Bank. Catwoman fights Poison Ivy and rids Wayne of her influence. On Saint Patrick's Day, Maroni's safe house is attacked by Holiday.

On April Fool's Day, both Batman and the Riddler attempt to determine who Holiday is. Batman suspects Holiday is Harvey Dent. The Riddler is employed by Falcone to determine Holiday's identity but can come to no firm conclusion. When the Riddler is kicked out of Falcone's office, Holiday shoots a number of bullets in an outline around the Riddler.

On Mother's Day, Scarecrow escapes from Arkham Asylum and poisons Batman with his fear gas. Gordon is still trying to find Wayne to confront him about his connections to Falcone. When Wayne sees Gordon in the streets, Wayne hallucinates that Gordon is the robber who killed Wayne's parents and flees. Wayne is arrested at his mother's grave.

In jail, Wayne recalls his father operating on Carmine Falcone at the request of Carmine's father. Holiday kills Maroni's father on Father's Day. Wayne is acquitted by a jury, which makes Dent believe justice is nothing but a coin flip. Falcone is employing Scarecrow and the Mad Hatter to break into Gotham City Bank Depository. Maroni offers to help Dent prosecute Falcone.

On Independence Day, Holiday kills the Gotham City Coroner. Falcone's daughter Sofia convinces Maroni to help Falcone attack Dent. Batman foils Scarecrow and The Mad Hatter's attempted robbery of the Gotham City Bank Depository.

During Maroni's trial, Dent wants Maroni to implicate Falcone, but instead Maroni throws acid in Dent's face. At the hospital Dent stabs his doctor and escapes. Falcone's sister Carla is killed by Holiday.

Batman goes looking for Dent because Batman believes Dent could be Holiday. Batman finds more evidence that Dent is Holiday at Dent's home. In an attempt to lure Holiday into the open, Gordon moves Maroni to a different cell, but on the way Maroni is shot by Alberto Falcone.

Batman and Gordon subdue Falcone, who confesses to all the Holiday killings. Falcone's penthouse is attacked by every villain in the book along with Dent, who has now taken on the identity of Two-Face. Batman intervenes and defeats all the villains, but not before Two-Face grabs Falcone and fatally shoots him. Dent turns himself in to Gordon and Batman but tells them there were two Holiday killers. Harvey Dent's wife Gilda explains to herself that she also committed a number of the Holiday killings.