“It is rare these days for Hongkongers to stand in line for any movie – let alone a local production – and it is heartening to see that a hunger for Cantonese-language cinema still exists,” wrote Post critic Paul Fonoroff on the film’s release.

The film’s 20th anniversary is being celebrated in a retrospective at this year’s Hong Kong International Film Festival, which is also screening its two sequels. All three films have been restored in 4K.

Infernal Affairs is more of a drama than a police actioner, and the action scenes are sparse and short.

The story revolves around a triad member (Andy Lau Tak-wah) who infiltrates the Criminal Investigation Bureau, and a police officer (Tony Leung Chiu-wai) who simultaneously goes undercover in his triad gang.

The police are led by Anthony Wong Chau-sang, who was then a regular in crime films, while Eric Tsang Chi-wai plays the gang boss.

Conflict ensues as both sides try to outwit each other to discover their respective moles. The twist is that Andy Lau’s character ultimately decides he likes life on the right side of the law, and is happy to kill anyone to keep his secret and remain a police officer.

“Infernal Affairs’ slick production values were far ahead of the local competition at the time, the casting was terrific, and there was a freshness in the way the film broke away from genre norms,” says Tim Youngs, the Hong Kong-based consultant for Italy’s Udine Far East Film Festival.

“But Infernal Affairs pushed harder by having multiple plants entrenched on both sides of the law, and it dropped the regular police-officer-film fights and chases in favour of intimate, character-driven drama and slow-building tension,” says Youngs.

“It drew on triad cinema too, but avoided clichéd scenes of gang war and posturing young thugs.”

Much of the success of the film came from having a strong script in place before shooting, something which had fallen out of favour amid the quick-fire production schedules of the late 1980s and early 1990s.

The casting was a big draw when the film opened in Hong Kong, and the filmmakers had cleverly covered all the bases with their choices. Not only did the film feature Andy Lau and Tony Leung, but their characters’ younger selves were played by teen idols Edison Chen Koon-hei and Shawn Yue Man-lok.

Pop icons Sammi Cheng Sau-man and Kelly Chen Wai-lam had supporting roles, as did Taiwanese singer Elva Hsiao, in a “particularly inconsequential part that would best have been left on the cutting room floor”, the Post noted.

Andrew Lau let Tony Leung and Andy Lau choose whether they played the villain or the hero, and they both chose the opposite of what he expected, although he went with their decisions.

“My responsibility in Infernal Affairs is the commercial element,” a modest Andy Lau said in an interview, “while Tony is there to provide the artistic element.”

“Their characters are well drawn and distinctive, playing off each other smoothly while both tackling inner turmoil,” says Youngs. “There’s a great deal of emotional complexity, and Lau and Leung both pull it off. Lau is cold and sinister, while Leung has warmth and melancholy, especially in some great scenes with Anthony Wong, Eric Tsang and Kelly Chen.”

There is a Buddhist backdrop to the storyline which is sometimes lost in translation. The Chinese title translates as “Continuous Path”, and the film’s final quote refers to avinci or “continuous hell”, one of the many Buddhist iterations of hell.

“It is the worst part of hell. Those who did great wrongs will be sent to continuous hell and experience great suffering,” said Andy Lau, who is a Buddhist. The relation of the title to the film is oblique, either referring to the life of deception the characters lead on earth, or to their punishment in the afterlife.

The film cost HK$40 million, and was a popular, critical and financial success, taking HK$43.7 million in 19 days at the local box office and winning seven prizes at the 2003 Hong Kong Film Awards, including best picture, best director and best screenplay. The film also pulled in around US$1.5 million for Hollywood’s remake rights.

“Infernal Affairs had top stars, arrived with a huge marketing push, and maintained consistently high-quality production values that competed with Hollywood fare. It scored incredibly positive word of mouth. Catching the film became a point of Hong Kong pride,” says Youngs.

“The burst of audience support carried Infernal Affairs II and III the next year, after the Sars crisis ended,” he adds. “But eventually local films were again too often dismissed at home as inferior.

“If filmmakers wanted the budget to match Infernal Affairs’ star power and pricey production standards, they increasingly looked to reach cinemas across the border through Hong Kong-mainland co-production.”

Infernal Affairs’ own mainland release, however, was not smooth. Censors there do not permit criminal characters to get away with their crimes – they must be seen to be punished.

“When the mainland authorities reviewed the film, they said it was unethical and could affect the audience in a negative way,” a spokesperson for Media Asia, the production company, told the Post. “They could not accept an ending where the bad guy gets away with murder.”

An alternative ending was therefore shot for the mainland release, and on early DVD releases, Hong Kong viewers were able to choose between watching the “ethical” Mandarin ending, and the “unethical” Cantonese version.

Film censorship is much stricter in Hong Kong today than it was in 2002, and it is anyone’s guess if it would still be possible to shoot a film about police corruption such as Infernal Affairs in the city in 2022.