SPL: Sha Po Lang (Chinese: 殺破狼, released in the United States as Kill Zone) is a 2005 Hong Kong action film directed by Wilson Yip and written by Yip, Szeto Kam-Yuen and Jack Ng. It stars Donnie Yen, Sammo Hung, Simon Yam, and Wu Jing. The film was released theatrically in Hong Kong on 18 November 2005.

Yam portrays a police detective who, suffering from cancer and about to retire, resorts to illegal means in order to catch a ruthless triad boss. The title Sha Po Lang refers to three words derived from Chinese astrology that each represent a different star capable of good or evil depending on their position in the heavens.

The prologue of the movie is set in 1994, prior to the return of Hong Kong to the People's Republic of China. Chan Kwok-chung (Simon Yam), a Hong Kong police inspector, has dedicated his career to putting Wong Po (Sammo Hung), a notorious triad boss, behind bars. While escorting a witness with damning evidence of Wong's wrongdoings to court, Chan's car is rammed by another car driven by Jack (Wu Jing), a ruthless assassin. Jack then executes the witness, ensuring Wong Po would walk free. Chan survives with a piece of glass stuck in his head. After the glass is removed, the doctor informs Chan of a tumor in his brain that will soon kill him. Chan becomes even more determined to bring down Wong Po, using any means necessary.

Three years later, Ma Kwun (Donnie Yen), a police officer from another precinct, is assigned to replace Chan, who is going to retire soon. Ma will lead Chan's team, composed of Wah, Sum and Lok. The three men are very protective of Chan, who has since adopted the slain witness' daughter, as her mother was killed in the earlier car crash.

An electronics shop owner brings to the police station a video tape of Wong Po torturing an undercover agent. In the video, Wong hits the agent repeatedly with a golf club, then one of his men finishes him off. Chan and his colleagues decide to alter the tape, intimidate the shop owner into accusing Wong Po of being the murderer, and eliminate the real killer. Ma, who once beat up a drug trafficker so badly that the latter became mentally handicapped, has vowed to abstain from using questionable means in his career. Ma notices that Chan's team is acting suspiciously, but he still helps in the arrest of Wong Po. Ma then catches Chan's team's in the act of murdering the henchman that actually killed the undercover agent. Ma briefly fights the four of them.

The group receives a message warning them against leaving the police station that night. Ignoring the threat, Lok goes to buy a gun to serve as Wong Po's "murder weapon", but is trapped in an enclosed area and ends up getting killed by a knife-wielding Jack. Meanwhile, a copy of the original video tape is given to Chan's superior, Cheung Chun-fei. Seeing that Chan had tampered with evidence to frame Wong Po, Cheung releases Wong and tries to arrest Chan. An elderly policeman called Uncle Ba (who had received help from Chan earlier in the film) helps Chan avoid arrest. Later that night, Jack sneaks up on Wah and Sum and stabs them to death. Ma rushes to save them but arrives too late. Before dying, Wah confesses to Ma that he, Sum and Lok had stolen money from Wong Po (when they busted one of Wong's drug operations earlier) to help Chan raise his adopted daughter, and were targeted for retaliation by Wong.

At the station, Ma has a heated argument with Cheung over the handling of the case. Furious, he turns in his badge and gun. Chan goes to Wong Po's office, pretending to bring the stolen money. He guns down several henchmen but is stabbed and overpowered by Jack, then tortured by Wong Po, who calls Ma and tells him that he has taken Chan captive.

Ma heads to Wong Po's office. Jack confronts and battles Ma in an alley. Jack wrestles Ma's baton away from him, but Ma eviscerates Jack with his own knife. In Wong's office, where Chan is tied up, Ma returns the money and fights Wong. The crime lord is seemingly defeated when he is slammed onto a glass display of bottles. Ma pours himself a drink, but Wong suddenly gets up and pushes Ma out of a window. Ma lands on the car carrying Wong's wife and baby son, caving in the roof. All three are killed instantly. Wong gazes down at Ma's body and recognizes the car underneath. Wong starts sobbing, broken with grief.