Inspector Lui Ming-chit, [Andy Lau], and his former classmate To Shing-bong, [Gordon Lam Ka-Tung], were school rivals who trained in judo together. When To is released from prison for robbery, he quickly re-joins Cao Nam and his gang to hijack an armored car transporting cash. [Lui Ming-chit], [Andy Lau], leads his squad to stop the break-in, and a tense gunfight erupts, during which Cao kills a female hostage. Cao and his crew escape after To suddenly rams Lui’s car, triggering a chase that ends with To’s arrest. He insists the crash was an accident and denies being Cao’s accomplice. He is released after his girlfriend Yin-bing, [Yao Chen], arrives with a lawyer to bail him out, but Lui orders his subordinates to tail him. Yin-bing promises To a fresh start and finds him a job in a restaurant.
The Regional Crime Unit soon discovers the corpse of one of Cao’s underlings and the burnt remains of the getaway vehicle. Lui leads a raid on Cao’s hideout after recognizing one of Cao’s men, Chow, in surveillance footage. A firefight erupts; Lui manages to capture Chow, while To and Cao escape. At Cao’s residence, the police attempt to arrest him because Chow could testify against Cao, but Chow destroys evidence and throws himself off a building, thwarting the arrest.
Lui enlists his longtime informant Tong Keung to go undercover inside Cao’s gang. Tong joins the next heist, but the gang grows suspicious and attacks Tong. They chase Tong to his house after finding a phone provided by Lui, and Lui arrives to pull Tong to safety too late—the gang has already shot Tong. They also throw Tong’s 10-year-old autistic daughter, Yiu-Yiu, [Jacqueline Chan], off a building, and she eventually succumbs to her injuries. Enraged, Lui confronts Cao, who is driving toward the airport; after a brutal struggle, Cao is arrested and officially charged with the murders of Tong and Yiu-Yiu, with blood and fabric particles found on Cao’s hand.
Lui later receives a clip from Yin-bing’s drug-addicted younger brother, Kit. The footage, captured from Cao’s car, appears to show that Lui had framed Cao by wiping Tong’s daughter’s blood on him. Lui confronts Kit, who tries to blackmail him for HK$500,000 a month; Kit suddenly suffers an asthma attack and dies after Lui refuses him an inhaler. Lui then removes all evidence from Kit’s apartment.
Meanwhile, Yin-bing breaks up with To after he’s implicated in the previous armored car heist. She lies that she’s two months pregnant with another man’s child. To tries to salvage the relationship by claiming to be an undercover cop, and he later informs Lui that the mastermind behind the prior armored car heist and the murders is Paco, Cao’s sworn brother who has just been released from prison. Paco is portrayed by Ray Lui.
To offers to become Lui’s informant in order to arrest Paco, on the condition that Lui tell Yin-bing about To’s undercover status. Lui agrees but does not plan to abandon Paco and the gang alive. Paco leads the gang in another armored car heist, armed with heavy weapons, turning the operation into a trap set by the police. A massive firefight erupts, drawing in Special Duties Unit officers and spilling into the Central District.
As the betrayal unfolds, To, who has been in contact with Lui via a live feed, phones Lui from a hostage’s device to coax him into letting To flee in a car. Lui urges him not to surrender, hoping the criminals will be taken out by the police. After an intense shootout, the gang is wiped out, and To escapes but is fatally struck by a passing truck. Yin-bing, watching the chaos unfold on television, breaks into tears.
In the aftermath, Lui writes a letter to Yin-bing, declaring that To was an undercover officer and that he will turn himself in for his illegal actions. After providing his testimony, Lui asks whether the storm is finally over, and the reply—“yes”—brings him a quiet sense of relief and a measure of gratitude.
