In year 689 of the Tang Dynasty, Wu Zetian (Carina Lau) is about to be crowned the first Empress in China despite opposition from Tang officials. To mark this occasion, she has a colossal Buddha figure built overlooking her palace. However, an official inspecting the Buddha's progress mysteriously erupts into flames. Pei Donglai (Deng Chao), an officer in the penal system, and his superior investigate and interrogates the supervising builder, a man named Shatuo, who was imprisoned and lost his hand after he took part in a rebellion 8 years ago. Pei's superior catches fire soon after in the palace courtyard in front of the Empress as she is overseeing her palace guards.
The Empress and her attendant Shangguan Jing'er (Li Bingbing) receive a message from the Imperial Abbot (state preceptor), who speaks through a magical deer. He says that Di Renjie (Andy Lau), who was jailed eight years ago after leading a rebellion against Wu, must be the one to solve the mystery of the fire. When Jing'er goes to fetch Di from prison, they are attacked by assassins.
Wu returns to Di his position as the royal detective, and charges him with solving the case of the phantom flame. She assigns Jing'er as his assistant to keep an eye on him. While staying at an inn, Jing'er tries to seduce Di on the Empress's orders but they end up facing more assassins. Di meets Prince Li, who is against Wu becoming Empress. Li tries to persuade Di to lead another rebellion: Di refuses. The next day Pei, who has been promoted, takes Di and Jing'er to inspect the charred remains of the officials and sees that a caged bird that was struck by one of the assassin's arrows the night before has caught on fire. Di finds that the arrows the assassins used contain a poison that ignites upon contact with sunlight, which was used to kill the two officials.
Pei joins Di in his investigation. During a visit to the Buddha, Di reunites with his friend Shatuo (Tony Leung Ka-fai). Shatuo suspects that the venom of insects called "fire beetles" was used to create the igniting poison. He points Di to a man called Donkey Wang, who is hiding in a network of caverns called the Phantom Bazaar. Pei orders Shatuo arrested for not telling him of this connection when he interrogated him before, but Di waves off the order saying that he can trust his old friend.
Di, Pei, and Jing'er find Wang at the Phantom Bazaar; however, they are pursued by a figure who seems to be the Imperial Abbot. Jing'er denies this and goes after him. Pei follows to help her but chases the figure out of the caves into the Infinity Monastery, the Imperial Abbot's residence. Intruders will be killed immediately, so Pei leaves and meets up with Jing'er, Di, and Donkey Wang. Donkey Wang reveals that he had been the court physician, and tried to use the fire beetles as medicine for the former Emperor. He flees when he discovers that the fire beetles are dangerous - their body excretes a liquid that catches fire when exposed to sunlight. Wang is able to use a process called transfiguration (based on acupoints) to change his appearance.
Prince Li finds Di and gives him back his mace, which has a special ability to shatter weapons. This mace was given to him by the previous Emperor but confiscated when he was imprisoned. Di maintains his political neutrality. Despite pressure from his subordinates, Li refuses to have Di killed, however Li is himself assassinated.
Wang had been raising the fire beetles in the Infinity Monastery, leading Di to suspect the Chaplain's involvement. Jing'er informs Wu of Di's intent. Wu meets Di outside the palace with Jing'er and her royal guards and warns him that he will be killed if he tries to enter the Monastery. Pei arrives and announces that Prince Li has been killed, allowing Di to escape.
Pei has a theory that the first official might have been killed because of something that turned up during his inspection of the Buddha statue. Pei visits his household and finds that his study was mysteriously burned to the ground. Luckily, the official moved his work to another room, and Pei finds that he had indeed discovered something in his inspection. He takes the diagrams, but is pursued and taken captive.
At the monastery, Di uncovers the fact that the Imperial Abbot is Jing'er using transfiguration as a disguise, and speculates that the Empress has used the figure of the Imperial Abbot as a way of justifying her tyranny with a supposedly divine source. He says that knowing the Empress's secrets puts Jing'er in danger. An anguished Jing'er attacks him, but finds herself unable to kill him in the end. She carries him out into the forest, where she trips several wires, releasing javelins which impale her. When he wakes up, Di fulfils her final request by sending her back to court and she dies in the Empress's arms.
Di then finds Pei in captivity. Pei erupts into flames immediately upon being exposed to sunlight. As he dies, he directs Di to look under his saddle, where he finds the diagrams. Di consults the diagrams and goes to the Buddha where he confronts Shatuo. Di discovers that Shatuo has been planning to kill the Empress by making the Buddha fall on the palace during the coronation. Shatuo admits that he intends to kill Wu for the mutilation and imprisonment he suffered. As the supervisor, he altered the Buddha's construction, adding two ducts to pour molten metal to melt the statue's foundations, and hollowing out two of the support beams so it would fall on the palace. He killed the two officials after they noticed the changes, and later killed Prince Li for insulting him. He also reveals that he had taken Prince Li's seal and had the late Prince's army ready to invade the city and kill Wu if she somehow survives. Shatuo sent Di to Wang as a distraction to give his assassins the opportunity to kill Di, while using their friendship to cast blame away from himself.
Di and Shatuo fight. Shatuo drenches Di in water poisoned by fire beetles. Shatuo reminds Di of the rebellion he led against Wu and questions why he is fighting to protect her. Di admits that she is evil but he cannot let her die, as all imperial officials will die and resulting chaos will harm the innocent. Workers start to pour the molten metal into the pillar to melt the base, and Di knocks one duct aside to change the direction of the fall. Infuriated, Shatuo fills a bottle of fire beetle water to assassinate the Empress and rushes to the coronation on horseback, however Di catches up with him and spills the water on Shatuo instead. Shatuo burns to death in the sun while Di manages to reach the coronation in time to save the Empress from the collapsing statue, and warn her of Prince Li's rebel army near the city. The Empress immediately ordered her generals to mobilize her own army that she had already assembled nearby to destroy the rebel army, demonstrating how clever and well-prepared she was. The Empress is grateful to Di for her rescue, and in return Di makes her promise to be a just ruler and to return power to the Tang Dynasty imperial family line after her reign is over. In year 689 of the Tang Dynasty, Wu Zetian (Carina Lau) is about to be crowned the first Empress in China despite opposition from Tang officials. To mark this occasion, she has a colossal Buddha figure built overlooking her palace. However, an official inspecting the Buddha's progress mysteriously erupts into flames. Pei Donglai (Deng Chao), an officer in the penal system, and his superior investigate and interrogates the supervising builder, a man named Shatuo, who was imprisoned and lost his hand after he took part in a rebellion 8 years ago. Pei's superior catches fire soon after in the palace courtyard in front of the Empress as she is overseeing her palace guards.
The Empress and her attendant Shangguan Jing'er (Li Bingbing) receive a message from the Imperial Abbot (state preceptor), who speaks through a magical deer. He says that Di Renjie (Andy Lau), who was jailed eight years ago after leading a rebellion against Wu, must be the one to solve the mystery of the fire. When Jing'er goes to fetch Di from prison, they are attacked by assassins.
Wu returns to Di his position as the royal detective, and charges him with solving the case of the phantom flame. She assigns Jing'er as his assistant to keep an eye on him. While staying at an inn, Jing'er tries to seduce Di on the Empress's orders but they end up facing more assassins. Di meets Prince Li, who is against Wu becoming Empress. Li tries to persuade Di to lead another rebellion: Di refuses. The next day Pei, who has been promoted, takes Di and Jing'er to inspect the charred remains of the officials and sees that a caged bird that was struck by one of the assassin's arrows the night before has caught on fire. Di finds that the arrows the assassins used contain a poison that ignites upon contact with sunlight, which was used to kill the two officials.
Pei joins Di in his investigation. During a visit to the Buddha, Di reunites with his friend Shatuo (Tony Leung Ka-fai). Shatuo suspects that the venom of insects called "fire beetles" was used to create the igniting poison. He points Di to a man called Donkey Wang, who is hiding in a network of caverns called the Phantom Bazaar. Pei orders Shatuo arrested for not telling him of this connection when he interrogated him before, but Di waves off the order saying that he can trust his old friend.
Di, Pei, and Jing'er find Wang at the Phantom Bazaar; however, they are pursued by a figure who seems to be the Imperial Abbot. Jing'er denies this and goes after him. Pei follows to help her but chases the figure out of the caves into the Infinity Monastery, the Imperial Abbot's residence. Intruders will be killed immediately, so Pei leaves and meets up with Jing'er, Di, and Donkey Wang. Donkey Wang reveals that he had been the court physician, and tried to use the fire beetles as medicine for the former Emperor. He flees when he discovers that the fire beetles are dangerous - their body excretes a liquid that catches fire when exposed to sunlight. Wang is able to use a process called transfiguration (based on acupoints) to change his appearance.
Prince Li finds Di and gives him back his mace, which has a special ability to shatter weapons. This mace was given to him by the previous Emperor but confiscated when he was imprisoned. Di maintains his political neutrality. Despite pressure from his subordinates, Li refuses to have Di killed, however Li is himself assassinated.
Wang had been raising the fire beetles in the Infinity Monastery, leading Di to suspect the Chaplain's involvement. Jing'er informs Wu of Di's intent. Wu meets Di outside the palace with Jing'er and her royal guards and warns him that he will be killed if he tries to enter the Monastery. Pei arrives and announces that Prince Li has been killed, allowing Di to escape.
Pei has a theory that the first official might have been killed because of something that turned up during his inspection of the Buddha statue. Pei visits his household and finds that his study was mysteriously burned to the ground. Luckily, the official moved his work to another room, and Pei finds that he had indeed discovered something in his inspection. He takes the diagrams, but is pursued and taken captive.
At the monastery, Di uncovers the fact that the Imperial Abbot is Jing'er using transfiguration as a disguise, and speculates that the Empress has used the figure of the Imperial Abbot as a way of justifying her tyranny with a supposedly divine source. He says that knowing the Empress's secrets puts Jing'er in danger. An anguished Jing'er attacks him, but finds herself unable to kill him in the end. She carries him out into the forest, where she trips several wires, releasing javelins which impale her. When he wakes up, Di fulfils her final request by sending her back to court and she dies in the Empress's arms.
Di then finds Pei in captivity. Pei erupts into flames immediately upon being exposed to sunlight. As he dies, he directs Di to look under his saddle, where he finds the diagrams. Di consults the diagrams and goes to the Buddha where he confronts Shatuo. Di discovers that Shatuo has been planning to kill the Empress by making the Buddha fall on the palace during the coronation. Shatuo admits that he intends to kill Wu for the mutilation and imprisonment he suffered. As the supervisor, he altered the Buddha's construction, adding two ducts to pour molten metal to melt the statue's foundations, and hollowing out two of the support beams so it would fall on the palace. He killed the two officials after they noticed the changes, and later killed Prince Li for insulting him. He also reveals that he had taken Prince Li's seal and had the late Prince's army ready to invade the city and kill Wu if she somehow survives. Shatuo sent Di to Wang as a distraction to give his assassins the opportunity to kill Di, while using their friendship to cast blame away from himself.
Di and Shatuo fight. Shatuo drenches Di in water poisoned by fire beetles. Shatuo reminds Di of the rebellion he led against Wu and questions why he is fighting to protect her. Di admits that she is evil but he cannot let her die, as all imperial officials will die and resulting chaos will harm the innocent. Workers start to pour the molten metal into the pillar to melt the base, and Di knocks one duct aside to change the direction of the fall. Infuriated, Shatuo fills a bottle of fire beetle water to assassinate the Empress and rushes to the coronation on horseback, however Di catches up with him and spills the water on Shatuo instead. Shatuo burns to death in the sun while Di manages to reach the coronation in time to save the Empress from the collapsing statue, and warn her of Prince Li's rebel army near the city. The Empress immediately ordered her generals to mobilize her own army that she had already assembled nearby to destroy the rebel army, demonstrating how clever and well-prepared she was. The Empress is grateful to Di for her rescue, and in return Di makes her promise to be a just ruler and to return power to the Tang Dynasty imperial family line after her reign is over.
Wu offers Di a place in her court, which he refuses. Di passes his mace to Wu resigning as inspector, and retreats into the Phantom Bazaar, where there is no sunlight. Donkey Wang informs him that there is very little chance that he will be able to cure Di of his fire beetle poison, and Di replies that despite this he is now at peace, and the two enter the Bazaar as the sun rises. The epilogue states that Wu reigned as the first and only Empress in China's history, and kept her promise to Di, abdicating after fifteen years on the throne, in favor of the Crown Prince, the son of the Tang emperor before Wu.
Wu offers Di a place in her court, which he refuses. Di passes his mace to Wu resigning as inspector, and retreats into the Phantom Bazaar, where there is no sunlight. Donkey Wang informs him that there is very little chance that he will be able to cure Di of his fire beetle poison, and Di replies that despite this he is now at peace, and the two enter the Bazaar as the sun rises. The epilogue states that Wu reigned as the first and only Empress in China's history, and kept her promise to Di, abdicating after fifteen years on the throne, in favor of the Crown Prince, the son of the Tang emperor before Wu.
