The Outbreak of Arkham Asylum and Monorail Battle was a mass breakout Arkham Asylum and failed terrorist attack on Gotham City via the release of Fear Toxin from the city's water supply carried out by the League of Shadows as their second method to destroy Gotham due to their belief that it had succumbed to decadence and corruption, and its destruction was necessary to restore the world to balance.
During his 30th birthday party at Wayne Manor, Bruce was confronted by a group of ninjas from the League of Shadows and his old mentor Henri Ducard, who then revealed himself to be the real Ra's al Ghul, the former who died being a decoy. Ra's, who had been conspiring with the Scarecrow the entire time, planned to destroy Gotham City by distributing the fear toxin (which was extracted by the Scarecrow from the League's blue flowers) undetected via Gotham's water supply, and then vaporize it with a microwave emitter stolen from Wayne Enterprises. Bruce, tricking his guests into leaving, fought briefly with Ra's while the League set fire to manor, then escaped the inferno with Alfred Pennyworth's help just as the manor was destroyed.
Meanwhile, at Arkham Asylum, members of the League disguised as SWAT members quickly took the Arkham staff, released all the inmates (including the Scarecrow) from their cells and made a hole in the wall leading into The Narrows with a bomb. Batman arrived to aid the police, who are engaged in battle with psychotic criminals that were set free just as Ra's started the toxins distribution on the same area. After saving his childhood friend Rachel Dawes and intimating his identity to her, he left Police Det. Sgt. Jim Gordon in control of the Tumbler to stop the elevated train that was being used to transport the vaporizer to the city's central water hub, located beneath Wayne Tower. Batman battled Ra's and overpowered him, then escaped just as Gordon toppled the elevated line using the Tumbler's missiles, leaving the train to crash to the ground in the Wayne Station parking lot with Ra's still aboard, killing him.