In the heart of Hong Kong, a nefarious terrorist group known as Vendetta, led by Ma Sai-kwan (codename Maverick) and an enigmatic figure referred to as Blizzard, ignites a wave of chaos by launching a catastrophic attack on the region's education bureau. In the wake of this upheaval, the police struggle to regain control with Poon Sing-fung, a former Explosive Ordnance Disposal officer turned mercenary, emerging as a key suspect. Once a celebrated member of the Hong Kong Police, Poon's career was tragically derailed when his superiors sidelined him out of fear of public backlash due to his prosthetic limb. Bearing a heavy heart filled with anger and a thirst for vengeance, he chooses to join forces with Vendetta.
Months later, Poon is spotted igniting a bomb inside a hotel, resulting in a devastating explosion that leaves him critically injured and slipping into unconsciousness. Upon awakening in a hospital bed, he struggles with amnesia about the harrowing events. During a police interrogation, he seizes an opportunity to escape. Meanwhile, the Counter Terrorism Response Unit's Chief Inspector Pong Ling and CID Chief Inspector Lee Yiu-sing work diligently to piece together the puzzle of the bombings and identify the elusive Blizzard, who seems to be in league with a shadowy figure known as Davy. Vendetta's agents attempt to capture Poon at the hospital but fall victim to Lee's counterattack.
As the investigation deepens, Pong confronts Poon, unveiling disturbing truths from his past—his impressive trajectory within the Explosive Ordnance Disposal Bureau (EODB), the disintegration of his rapport with his superiors, and a harsh critique that marred the police force's public image. In a shocking twist, Pong reveals that Poon himself is Blizzard, the mastermind behind Vendetta's attacks. Reeling from this revelation, Poon finds himself ensnared in Pong's intricate scheme, which she claims is a covert operation aimed at reinstating Poon's tarnished name. She shares this information with Tung Cheuk-man, another EOD officer and Poon’s closest ally, who finds himself torn between allegiance to Poon and moral indignation over Pong's controversial tactics. Amid rising tensions, Pong argues that her means are justified to secure leniency for Poon from the Hong Kong Supreme Court, in light of his role in the bombings.
As Poon receives a cryptic message from Al-Qaeda, cleverly concealed within an inspirational magazine, he convenes with Ma Sai-kwan and the Vendetta members—codenamed Money, Slave, Sniper, and Rhino—to strategize their next brutal strike. Under Ma's guidance, Sniper is tasked with placing a bomb aimed at rupturing gas pipelines in downtown Hong Kong, threatening extensive destruction. Meanwhile, Inspector Lee, Tung, Pong, and Poon’s former EODB colleagues, Lun Ting-pong and Chan King-to, rush to the imminent danger.
Upon arrival, Sniper takes vengeance by severely injuring Chan, who ultimately succumbs despite desperate rescue efforts. Fortunately, Tung survives clad in armor. While Pong’s team attempts to neutralize Sniper from a distance, they face formidable resistance from his skills. In a last-ditch effort to outsmart their foe, they adopt guerrilla warfare tactics and ultimately take Sniper down. Tragically, Chan's life slips away, adding to the weight of their mission.
Poon's covert meetings with Pong become evident, provoking Vendetta to ensnare him in a psychological game called Mastermind. Ma seeks to extract Poon's true identity before deciding his fate. As Pong and Tung rush to rescue Poon, they initially stumble due to the intricately devised trap. However, as Poon’s memories resurface, he recalls the crucial combination needed to escape. With mere seconds left, Tung frees Poon, revealing the harrowing news: Vendetta plans to detonate a 10-20 ton nuclear warhead, dubbed Davy, at the International Finance Centre (IFC) and Hong Kong Airport.
The stakes escalate dramatically as Ma coordinates a simulcast attack on the IFC, Hong Kong MTR, and Airport Express train, commandeering a train packed with explosives and hostages. Meanwhile, Fat Sze and Lun manage to disarm the treacherous van in the IFC parking area, eliminating Money and Slave in the process.
Inspector Lee swiftly arrives, neutralizing Vendetta operatives and establishing control of the scene. As Lun hatches a daring plan to intercept the bomb-laden train, his strategy involves ramming it into the water, thus destroying the Tsing Ma Bridge to limit damage.
Pong and her CTRU teams execute a successful raid on the control station, taking down Rhino's men but not without a last desperate act from Rhino, who chooses to end his life. As tensions subside, Poon's colleagues have thwarted another Vendetta plot, though questions linger about the toll it has taken.
The fateful day sees Poon and Tung devise a meticulous plan, positioning a rigged van with strategic precision. Tung escapes in a helicopter, leaving Poon behind, who seeks redemption for his involvement in past terror attacks. In a heart-wrenching farewell to Pong, Poon willingly embraces his fate to obliterate the bridge and avert disaster for Hong Kong’s shores. As Ma's train collides with the severed bridge, it tumbles into the depths, culminating in a spectacular explosion that claims the lives of both Poon and Ma, sending reverberations through the city's underwater currents and ultimately safeguarding it from a catastrophic aftermath.
As Tung and Lun mourn their fallen comrade, Pong grapples with the profound cost of Poon's sacrifice, her tears mingling with uncertainty about whether their endeavors justified the ultimate price paid. In the poignant aftermath, Pong begs a neurologist to erase all memories of Poon's involvement from her mind except for one defining moment. She recalls their serendipitous meeting during a police dinner, when Poon intentionally spilled red wine on her uniform to catch her attention, a fleeting scene that resonates as a lasting reminder of his profound impact on her life.
