In the third year of the Tianbao Era, operatives of Wolf Squad disguise themselves as merchants amidst the hustle and bustle in the western district of Chang’an city on the eve of the Lantern Festival. The operatives are waiting for the right moment to strike. Li Bi, director of Peacekeeper Corps, is under orders to apprehend the Wolf operatives that have infiltrated Chang’an. This covert operation is foiled, allowing the squad leader Cao Poyan to slip away. Li Bi sends Tan Qi to the jail to bring the convict Zhang Xiaojing, who is sentenced to death, to be tasked with continuing the investigation.

Zhang Xiaojing is about to chase Cao Poyan when Cui Qi discloses Li Bi’s true motive to him. Li Bi creates a diversion to lead the others away, leaving only Zhang Xiaojing behind. He tells Zhang Xiaojing that he wants to be the nation’s Grand Chancellor. Li Bi tells Zhang Xiaojing that while he cannot lift the death sentence, he can allow him to work as a mercenary lieutenant for one more day. Li Bi reports to his superior He Zhizheng about Zhang Xiaojing’s, and through a chance encounter he finds out that the Emperor wants to hand over power to Counsellor Lin Jiulang.

Mayor Ji Wen of Xinfeng County gets wind from a mole inside Peacekeeper Corps of another of the Crown Prince’s wrongdoings. Lin Jiulang wants to use it to remove the Crown Prince’s status as heir to the throne. Zhang Xiaojing maintains pursuit of Tugelu, who out of desperation holds a boy hostage, claims to have the map of Chang’an in his possession, and demands that Chang’an residents drive away Zhang Xiaojing. Li Bi finds out that the operative has been beaten to death, the map has been lost, and Lizheng of the Huaiyuan district has been killed.

Wolf Squad’s real intention is to commit arson. Zhang Xiaojing becomes restless, Tan Qi realises his state of mind and reports it to Li Bi. He Zhizheng volunteers to undergo a baptism of fire on Zhang Xiaojing’s behalf, forcing the Religion and Race ministers to stay put and not make any move. Tan Qi finds out that the Shadow Woman is dead, which means the evidence implicating Lin Jiulang has died with her. Commander Chen of the Longwu Regiment and Commander Zhao of the Yourao Regiment barge into Peacekeeper Corps together to force Li Bi to hand over his Directorship Badge for the agency.

Long Bo hides in Li’s General Store in the Changming district. Yu Chang steals a map off Tugelu amidst the mayhem and hands it to Long Bo. Xu Bin finds out that Long Bo has a VIP pass for a brothel, and Zhang Xiaojing decides to talk to someone knowledgeable in brothels and related matters. Knowing that Zhang Xiaojing is overwhelmed with problems on many fronts, Feng Dalun, an official from the Ministry of Works, sends Qin Yu, a gangster from the local Blaze Gang, to fight Zhang Xiaojing. Tan Qi soon finds out that the fragrance emanating from the Shadow Woman relates to Wen Ran.

Zhang Xiaojing wants to invite Ge Lao, who oversees all illegal trade in Chang’an, to assist with the investigation. Ge Lao demands that Zhang Xiaojing hands over the mole. Zhang Xiaojing sells out Xiao Yi, for which he loses the support of all mercenaries in Chang’an. Ge Lao discloses the fact that a prostitute called Tong’er is the issuer of the VIP pass, and he happens to hold her imprisoned. Tong’er tells Zhang Xiaojing that she would only disclose Long Bo’s hideout if Ge Lao is prepared to free her and her lover. Ge Lao refuses to set them free.

Zhang Xiaojing reluctantly exposes Tong’er’s lover. Tong’er tells of the location of a residence where Long Bo once took her. Zhang Xiaojing, excitedly leaves for the place, only to be threatened by the mercenaries in Chang’an. The insubordination means there is no one he can deploy, and Yao Runeng also forsakes him under a vague pretext. With the time for the handover of Peacekeeper Corps fast approaching, Li Bi accepts the blame in Lin Jiulang’s residence in exchange for the right to investigate the case for one more day.

Wen Ran tells Zhang Xiaojing that everything she has been doing is to help him escape from prison. She hopes he will stop the investigation. Zhang Xiaojing pretends to go along with it, then barges into Wolf Squad’s mansion on his own. He challenges the operatives, one of whom, Mageer, turns the tables by threatening to kill Wang Yunxiu, leading to Zhang Xiaojing being captured instead. Cui Qi leads the Lyuben Regiment to aid Zhang Xiaojing, only to be held up by the Lantern Festival floats.

Zhang Xiaojing draws a map of Lin Jiulang’s mansion for Wolf Squad and advises them to launch their strike here. Lin Jiulang becomes suspicious of the vendetta between Zhang Xiaojing and Blaze Gang. After looking into it closely, it is revealed that Wen Wuji was killed as a result of hiring members of Blaze Gang. Filled with rage, Zhang Xiaojing slaughters 34 members of Blaze Gang. Lin Jiulang tells the Blaze gangsters to go to the mansion in Xiuzheng district to kill Zhang Xiaojing amid the mayhem.

Zhang Xiaojing drives a wedge between Wolf Squad and Blaze Gang, which leads to a melee between the two camps and buys Zhang Xiaojing enough time until Cui Qi and his Lyuben Regiment support arrives. The melee ends with Blaze Gang fleeing and most of the 50 operatives of Wolf Squad killed. Zhang Xiaojing is wounded and unconscious while Wen Ran is taken away by Mageer and squad leader Cao Poyan, who had slipped away from the melee. Earlier, Cui Qi lies that Wolf Squad has been completed eliminated, in order to spare the Lyuben Regiment from any disciplinary sanctions.

Tan Qi is yet to report back, Yao Runeng advises Li Bi that the case must be finalised. Li Bi worries that things are not as reported. Tan Qi sends a message back from a watchtower saying that two operatives of Wolf Squad have escaped and are still at large. Wen Ran agrees to take the Wolf operatives to see the instigator of today’s operation. The Crown Prince had hoped Guo Lishi would talk the Emperor out of handing over power to Lin Jiulang before the start of the imperial banquet. But Lin Jiulang masterfully sows discord between the Emperor and Guo Lishi through Yan Yuhuan.

Luda and Ruige from Nobleman Yousha’s entourage chases an outstanding debt, only to suffer defeat at the hands of Yu Chang. Li Bi arranges for the rebel fighters to get away, and to put explosives in place at the warehouse. He leaves Cao Poyan and other operatives there as bait. Tan Qi does as Zhang Xiaojing tells her, to hint that Prince Yong should make Blaze Gang release the girl they abducted. Prince Yong directs Feng Dalun to go and apprehend Zhang Xiaojing. Zhang Xiaojing follows a lead that takes him to a quiet area in Changming district.

Yu Chang rushes to the fake house to confront Zhang Xiaojing. He promises to disclose Wen Ran’s whereabouts to fool Zhang Xiaojing into sending a signal to lead astray the Lyuben Regiment chasing them. Wang Yunxiu tells Yuan Zai that she witnessed Zhang Xiaojing drawing a map of Counsellor Lin’s mansion for Wolf Squad. Yuan Zai reports the intelligence to Counsellor Lin to take credit for it. Cui Qi leads the Lyuben Regiment to an empty house and Zhang

News of the explosion in Changming district travels back to Peacekeeper Corps. Li Bi learns that "stone grease" is an expression referring to the explosives. Research at the Security Bureau reveals that Xu Bin and Zhang Xiaojing in fact know each other. Li Bi suspects Zhang Xiaojing intentionally led Wolf Squad to the Counsellor’s mansion as a way to get even with him. Lin Jiulang secretly sends a message to the Emperor accusing the Crown Prince of four serious crimes. The Crown Prince finds out about the accusation against him and looks to Li Bi to solve the case as soon as possible to vindicate his name.

Worried that he may be assassinated, Lin Jiulang refuses to attend the banquet and assigns Ji Wen to find out everything about Xu Bin, the Security Office researcher. Li Bi follows Xu Bin to a secluded factory in Huaiyuan district, and discovers to his surprise that this factory of Xu Bin’s is a paper mill hidden in a secluded location. Xu Bin tells Li Bi the truth. Touched by his sincerity, Li Bi is no longer suspicious of Xu Bin. Lin Jiulang’s investigation reveals that He Zhizheng’s dim-witted son once secretly gave Xu Bin a large sum of money, which leads him to suspect that He Zhizheng is also involved in the plot.

With the help of surveillance conducted at watchtowers set up by Peacekeeper Corps, Zhang Xiaojing enters into intense close combat with the enemy, finally eliminating a Wolf operative and a horse carriage. Li Bi tries to dispatch soldiers to help Zhang Xiaojing in pursuing Wolf Squad, and clears the crowd from roads near Peacekeeper Corps headquarters. He prepares to act as bait to lure the enemy in. Zhang Xiaojing finally subdues Mageer and crashes the horse carriage with the explosives into a lake.

Guo Lishi delivers an oral edict from the Emperor ordering Peacekeeper Corps to close the investigation. The edict states that all personnel in the Agency are deemed to have achieved sufficient merits to be safe from any disciplinary sanctions. They shall return to the original posts from which they were seconded. Zhang Xiaojing is to be sent back to death row. Li Bi secretly orders Tan Qi to release Zhang Xiaojing to undertake further covert investigations. However, having been deceived and misguided by Yao Runeng, Cui Qi leads the Lyuben Regiment to defect to the Yourao Regiment, taking Zhang Xiaojing with them.

Li Bi arrives at He Zhizheng’s mansion to find it eerily quiet. Unbeknown to Li Bi, all the servants at the mansion have died in mysterious circumstances in the firewood shed. With no news from Li Bi after an extended wait, Tan Qi makes a daring attempt to lie her way into the Yourao Regiment to rescue Zhang Xiaojing. Zhang Xiaojing devises a plan to burn down the barracks of the Yourao Regiment to create an opportunity for the three of them to escape. They run into Cui Qi as they head to the exit, and are surrounded.

Zhang Xiaojing and others are in a formidable battle with the Yourao Regiment. General Gan Shoucheng of the Yourao Regiment zeros in on the three of them with strong forces and successfully captures them. Tan Qi puts aside her dignity and dances as a slave girl for the pleasure of Gan Shoucheng in order to buy time for Zhang Xiaojing and Yao Runeng. Li Bi pretends to be dead to escape capture. He then asks Guo Lishi for urgent assistance. Guo Shili risks making himself an enemy of the Yourao Regiment to try and save Zhang Xiaojing, Tan Qi and Yao Runeng, and finally succeeds in rescuing them.

Yao Runeng remains suspicious of the relationship between Zhang Xiaojing and Wen Ran. Zhang Xiaojing comes clean about this relationship, and Yao Runeng decides to release Wen Ran from Peacekeeper Corps’s custody. Li Bi tells Cao Poyan that Wolf Squad have been used as pawns, which crushes Cao Poyan’s loyalty to his master. Cao Poyan finally gives up the key person, the nobleman Yousha, and hints about a cross-shaped lotus which can be found at his hideout. Zhang Xiaojing and Tan Qi go to the Nestorian Church to look for Yousha, but the priest Yisi at the Nestorian Church realises their deception and locks them in the confessional.

Zhang Xiaojing breaks into Puzhe’s room and catches a glimpse of the fleeing assassin. He gives chase, and is followed by Yisi. The assassin is not alone, he and his accomplice create a commotion and flee amidst the chaos. At the suggestion of Tan Qi, they make an announcement that Puzhe is still alive and is being sent to the clinic for treatment. The assassin impersonates a medic and comes to the clinic to intercept Puzhe, only to be captured by Zhang Xiaojing. Yu Chang comes to the Nestorian Church to silence them by making an attempt on their lives.

Lin Jiulang gets wind of Guo Lishi openly supporting Peacekeeper Corps and decides to seize this opportunity to level trumped up charges against the Crown Prince, He Zhizheng and Guo Lishi in a power-grab manoeuvre. Guo Lishi comes up with a daring plan of saving everyone by capturing He Fu and making him confess to acting alone. He Fu flees to Long Bo’s hideout and urges him to bring his plan forward. Long Bo refuses. He Fu tells him that Yu Chang is already in custody at Peacekeeper Corps. Li Bi and Xu Bin’s investigation reveals that Yu Chang is Long Bo’s accomplice.

Li Bi interrogates Yu Chang, who not only remains tight-lipped but nearly kills him. Zhang Xiaojing, Tan Qi and Yisi go to Liu’s Bookshop to investigate further. Zhang Xiaojing tells Tan Qi and Yisi that when the Battle of Fort Beacon ended years ago, there were in fact eight survivors from the Eighth Squad. However, with the exception of Wen Wuji, their whereabouts remain unknown. Long Bo and the rebel fighters break into an unguarded Peacekeeper Corps, rescue Yu Chang, and barge into the main hall and slaughter all the Bureau officials.

Zhang Xiaojing, Tan Qi and Yisi go to Liu’s Bookshop. The person who answers the door at the bookshop is the Fire Master of a paramilitary organisation and Zhang Xiaojing’s former comrade-in-arms, Ding Laosan. Long Bo safely retreats from Peacekeeper Corps with Yu Chang and the rebel fighters. Mass casualties and the intense blaze turn Peacekeeper Corps into an inferno, burning every file in the archives to ashes. Li Bi mixes with the crowd and continues to track the paramilitaries, not realising that Long Bo is following his every move.

The paramilitaries mistakenly believe that their Fire Master Ding Laosan has been killed by Zhang Xiaojing. Subsequently, a call goes out urging their comrades in the city to hunt down and kill Zhang Xiaojing. Li Bi is detained by Long Bo in his hideout mansion. Li Bi then sees a message from the watchtower announcing that Zhang Xiaojing is a wanted fugitive. The message sends him into despair. He Fu urges Long Bo to assassinate Lin Jiulang, which prompts Long Bo to lash out at him. Tan Qi comes up with a clever plan that tricks the ordinary mercenary soldiers into helping Zhang Xiaojing.

With his eyes gouged out, He Fu is locked up with Li Bi. Li Bi questions him about whether He Zhizheng was behind the plot to assassinate Lin Jiulang. He Fu tells him to ask He Zhizheng himself. Long Bo sends Wen Ran to kill Li Bi, who in desperation says that he is the only person that can make sure that Zhang Xiaojing stays alive, but he must be allowed to return to Peacekeeper Corps. Li Bi lists some of He Fu’s crimes, He Zhizheng tries to protect He Fu, and Li Bi wants to know whether it was He Zhizheng or the Crown Prince behind everything.

Lin Jiulang interrogates He Fu over the reason for the assassination and demands that he implicates He Zhizheng and the Crown Prince. He Fu remains tight-lipped and insists on staying silent until he is formally tried in a court of law. Li Bi is imprisoned in a dungeon in the underground city of Pingkang district. Despite repeated requests to be released to carry on with his investigation and save hundreds of thousands of lives in Chang’an, his words are dismissed by the jailers as nonsense.

Zhang Xiaojing runs into Li Bi by chance in the underground city. The two of them go over what has happened and come to the conclusion that Long Bo’s assassination of Lin Jiulang is just an act. Zhang Xiaojing comes to Ge Lao to talk business, and Ma Tailang seizes this moment to rebel, proposing that he and Zhang Xiaojing work together to kill Ge Lao. Zhang Xiaojing had long heard stories about Ma Tailang ransacking the homes of spies who had fled.

Zhang Xiaojing goes to Liu’s Bookshop with the pass that Ge Lao gave him to see the acting Fire Master. Ge Lao has absolute authority over the paramilitaries since he is their sole source of intelligence. Zhang Xiaojing follows the lead provided by the acting Fire Master to retrieve the deed, only to find that it has been destroyed. He demands an answer and eventually learns that Yu Chang burned the deed. Li Bi asks Guo Lishi to try to locate Mao Shun to find out who owns a mansion with a self-cooling room.

In a flashback, Li Bi wants to stay in the mountains to practice monasticism, and when Yao Runeng tries to talk him out of it, they have a quarrel and Li Bi gets rid of him. He Zhizheng wails when he finds out that He Fu’s eyes have been gouged out. He Fu falsely accuses the Crown Price of ordering him to assassinate Lin Jiulang, and states repeatedly that He Zhizheng is innocent. Lin Jiulang affixes all three of the official seals onto He Fu’s statement and submits it to the Emperor.

Li Bi recalls Xu Bin once said that the key to resolving issues is to stay alive. He wants to free Tan Qi and then accuse Lin Jiulang for acting ultra vires by exercising authority on behalf of all three government ministries. He signs the statement with great reluctance. Tan Qi stays in the Counsellor’s mansion as hostage while Li Bi is allowed to leave. Li Bi bids Tan Qi farewell, and she senses his stoicism. Zhang Xiaojing goes to the paper mill, hands the foreman a slip, and moments later Xu Bin appears.

Li Bi suspects the Emperor wants to use the struggle between Lin Jiulang and the Crown Prince to even up their power and stabilise the Emperor’s own power. Guo Lishi immediately orders him to be quiet. Li Bi goes to see the Crown Prince and explains why he signed the statement. He pleads with the Crown Prince to rescue Tan Qi. Guo Lishi follows the Emperor’s order to deliver a cheap set of clothing to Lin Jiulang for him to wear to the lantern banquet. Li Sifang tells Yao Runeng to eliminate Tan Qi.

A seriously wounded Yao Runeng is ditched in the street. A mysterious man appears to take him away and promises him to make him the pride of his family. Tan Qi is grateful to Li Bi for saving her life, but she holds a grudge against him. Li Bi apologises and explains that he was left with no choice but to save the Crown Prince at her expense. Tan Qi begs Li Bi to plead with the Emperor to spare Zhang Xiaojing’s life. Li Bi feels that saving the Crown Prince must be the priority.

Rebel fighters pretend to be craftsmen, Zhang Luo smells a rat and decides to check things out, only to be pushed into the river by them. The craftsman studies the fragments from Zhang Xiaojing closely and comes to the conclusion that they are from bamboo sticks used to build the Heavenly Lantern Tower, and that Long Bo could fill them with stone grease and make the Lantern Tower a 50-metre explosive. If detonated, it would instantly destroy everything within a few kilometres.

Tan Qi begs Yan Yuhuan to plead with the Emperor to spare Zhang Xiaojing’s life by lying about Zhang Xiaojing being her lover. Yan Yuhuan grudgingly agrees. Lin Jiulang and Prince Yong both try to claim credit and the Emperor rebukes the Crown Prince for his incompetence. He Zhizheng steps forward to get the Crown Prince out of a jam by revealing that the land on which an embassy was built was forcibly acquired from its rightful owner. In a flashback, Wen Wuji meets with Blaze Gang but the negotiations break down and Wen Wuji is killed.

The Crown Prince and Lin Jiulang enter into a heated exchange, both trying to assign blame to each other. This scene confirms the Emperor’s suspicion that the Crown Prince ordered He Fu to assassinate Lin Jiulang. Long Bo brags to Li Bi about what he believes to be his flawless assassination plan. Li Bi is only interested in finding out who the mastermind is. The Emperor forces He Zhizheng to pass judgement on whether the Crown Prince is an innocent person facing false accusations.

The Emperor gazes at the magnificent Great Taoist Lantern and marvels at Mao Shun’s impressive design. Zhang Xiaojing is utterly baffled why Mao Shun would collaborate with Long Bo in making this destructive Lantern. Mao Shun tells of his reasons. The Emperor tells the Crown Prince to personally serve meat for everyone at the feast, and tells the Crown Prince to serve Lin Jiulang’s portion first. He offers the meat to Lin Jiulang, who lies about having to go to the toilet as he is scared of eating meat from the Crown Prince.

The survivors’ only wish was to return to Chang’an to reunite with their families. Cold and hungry, Wen Wuji began telling them about the delicacies of Chang’an to help alleviate their hunger. The Deputy Minister announces that the Lantern Festival banquet has commenced, and both officials and civilians begin to enjoy the wondrous lanterns. The sight triggers memories of the catastrophic Battle of Fort Beacon for Zhang Xiaojing. Soldiers of the Eighth Squad had run out of food.

The enemy’s 3000-strong reinforcement soon arrived at Fort Beacon. By now, only 13 of the Eighth Squad were left. Ding Laosan raised his sword to call for a final charge. Zhang Xiaojing recalls how the enemies were blown up by explosives then, and is disturbed by the mental images of that deadly explosion. Despite being affected by these traumatic memories, he pulls himself together to try to stop Long Bo, who in fact turns out to be Xiao Gui, his comrade-in-arms from the Eighth Squad.

He Zhizheng fearlessly reminds the Emperor that a ruler who mistreats his own children can never be a great patriarch for his subjects, as an Emperor is expected to be. These frank words of caution ring alarm bells for the Emperor. Zhang Xiaojing is shocked by the revelation that the ruthless killer standing in front of him is his comrade-in-arms from the Eighth Squad, Xiao Gui. This reunion of two old friends is filled with enmity. Long Bo forces Zhang Xiaojing to kill Li Bi. The circumstances allow no time for Zhang Xiaojing to consider his next move.

The Emperor publicly puts the Crown Prince in a conundrum. Not knowing what to do, he drops to his knees and asks to be excused under the pretext of being overcome. The Emperor makes no attempt to stop him. Lin Jiulang seizes the opportunity to smear the Crown Prince by claiming that his retirement from the banquet is a violation of solemn rites. He Zhizheng speaks in support of the Crown Prince and tries to assassinate Lin Jiulang, not knowing that he is wearing the brigandine gifted to him by the Emperor.

The Emperor empathises with He Zhizheng’s patriotism for Great Tang and his heartfelt support and affection for the Crown Prince, and decides not to hold his actions against him. Seeing the Emperor’s resolve to revive Great Tang puts He Zhizheng to shame, and he drops to his knees and asks to be dealt with for his crime. Zhang Xiaojing wants to remove the Lantern Tower’s extendable arms. Yu Chang regains consciousness and they begin fighting again, and Yu Chang is completely overpowered by Zhang Xiaojing due to exhaustion.

Long Bo leads the Emperor through the secret passage. Lin Jiulang and other officials lucky enough to have escaped are rescued by Yuan Zai. Guo Lishi lies about the Emperor being safe in order to calm the people. The Crown Prince dispatches a large search party to locate the Emperor. Meanwhile, Li Jingzhong urges the Crown Prince to announce his ascension to the throne to ensure that rule does not fall into someone else’s hands. A group of bureaucrats led by Wang Hong urges Lin Jiulang to act as regent.

The copyist Zhu Ci from the Ministry of Revenue and his wife and son Zhu Xuan bring relief goods to the residents of a slum in Pingkang district. Zhu Xuan see the Emperor lying battered and injured by the road, beaten by a low-ranking bureaucrat. Zhu Xuan brings his parents over, they help the Emperor onto the horse carriage so he can ride home, only to be suspected by the Emperor of acting with ulterior motives.

Gan Shoucheng is determined that the Crown Prince be put to death, but He Zhizheng and Ning Wangsun come to the rescue. He Zhizheng castigates Gan Shoucheng, who drops to his knees at once and vows to support the Crown Prince wholeheartedly before retreating with his men. Li Bi returns to Peacekeeper Corps, Ji Wen orders Commander Zhao to kill Li Bi. Afterwards he feels conflicted about that and decides to temporarily lock up Li Bi instead.

Cheng Can proposes that the investigation be carried out as suggested by Li Bi, and whoever turns out to be the perpetrator must be severely punished. He Zhizheng approves. Zhang Xiaojing is reminded of the tragic death of Wen Ran and is overcome with grief. Long Bo tells the Emperor in great detail of the many interesting stories between him and Wen Wuji, as well as how Wen Wuji risked his own life to save him on the battlefield. Long Bo cries out that he is Xiao Gui, the Banner Guard of the Eighth Squad of the Anxi Iron Army of Longyou County.

Cheng Can believes that Long Bo used the assassination of Lin Jiulang as a pretense, that his real goal was to use He Fu’s desperation to seek revenge to plot an assassination of the Emperor. The assassination was to be carried out by a meticulous plan of blowing up the Heavenly Lantern Tower. Mao Shun’s draft drawing of the Lantern Tower has a line of words in fine print in handwriting similar to He Zhizheng’s. However, the fire at the archive destroyed everything so there is nothing there to corroborate this theory.

The Emperor believes firmly that the Crown Prince was the mastermind behind Xu Bin, that he brags about himself being an ideal candidate for the job of Counsellor, and he planned to assassinate the Emperor. Xu Bin points out that the Emperor wrongly places his trust in people with bad motives, and that leads to corruption and mismanagement. He rebukes the Emperor for having Lin Jiulang in his employ. The Emperor finally realises that Xu Bin has gone to great lengths to look out for the Emperor’s interests.