Cao Baoping is visibly nervous as he emerges from the wings of San Sebastian's Principe cinema and ambles centre stage. Unlike most directors at the Spanish city's film festival this year to present their latest work, the Shanxi-born, Beijing-based filmmaker spends most of his short speech pleading with the audience to 'be patient' with his film. 'It's not exactly the type of Chinese film which travels to film festivals,' says Cao, who for the past two decades has been a lecturer at the Beijing Film Academy. His apprehension is understandable. The Equation of Love and Death lacks gravity-defying action choreography - an element most non-Chinese viewers associate with Chinese cinema these days. Nor does it offer the gritty realism that has propelled many a mainland filmmaker to award-winning fame in the festival circuit. His film features a crabby female taxi driver searching for a lover who's been missing for four years, a botched drug deal involving two country bumpkins, hair-raising chaos on the motorways of Kunming, and handwriting tests which could have come straight out of a crime thriller. 'This film travels in the terrain lying between the strictly commercial and the arthouse,' says Cao, speaking more than a day after his anxiety-riven pre-screening talk. He appears more self-assured than he did before the Spanish audience, his confidence strengthened by the best new director award he had received two hours earlier from fellow Chinese filmmaker Joan Chen, who headed the prize's jury. The award gives Equation the boost it needs to secure slots at other international festivals and adds to the commercial success it's enjoyed. The film generated box office receipts of 12 million yuan (HK$13.7 million) in its first week of release, meaning the financial outlay of 10 million yuan has already been recouped. And that was before the win at San Sebastian. Cao admits he's pleasantly surprised by the excellent reception the film has had at home and abroad. He believes Equation hardly adheres to the paths trodden by his compatriots such as Zhang Yimou, Chen Kaige and Jia Zhangke. Equation isn't an epic that revisits ancient Chinese history (such as Hero or Curse of the Golden Flower) nor is it a mournful saga charting the march towards a capitalist new age (Platform or Still Life). Instead, the film mixes elements usually found in suspense thrillers, such as an abduction at gun-point which goes awry on a deserted country road, with a colour scheme (gloomy greyish hues) and editing that would be more at home in off-kilter cinematic fare. The film opens with a series of cuts of its protagonist, the taxi driver played by Zhou Xun, nervously talking to herself about the meaning of a series of random numbers that turn out to be the days on which she received letters from her vanished fiance. Seen through the prism of the film's Chinese title, Li Mi De Cai Xiang (Li Mi's Conjecture), the opening sequence might lead the viewer to expect the ensuing 96 minutes to be about the protagonist's pursuit of her long-lost partner. Such an impression tends to grow as she foists his photographs on her passengers, among them Qiu Huokuai (Wang Yanhui) and Qiu Shuitian (Wang Baoqiang), two villagers whose awkward behaviour betrays a sinister motive behind their hurry to get to Guangzhou. Their paths eventually cross with another taxi driver, Ma Bing (Deng Chao), over a traffic accident: a seemingly insane poet jumps off a bridge and lands on Ma's car. It's a suicide which sparks off a story of coincidences, disturbed consciences and failed attempts at committing a capital crime. All this eventually leads to the discovery of the truth behind the disappearance of the protagonist's partner. The process is overseen by an upstanding police officer, Ye Qingcheng (Zhang Hanyu). It's not the first time that Cao has used honorable Chinese policemen to end his stories. In Trouble Makers, his debut feature from 2004, the police arrive at the scene just when the film's villains are ready to defeat the bungling operation a lowly official launches against them. In Equation, the police's knowledge of the dirty deals going on, and officer Ye's efforts to save Li Mi's sanity, radiate a strong belief in the force's role as guardians of society. Cao admits he's made some compromises to bring his idea to fruition. 'You are responsible for a lot of investment people made, after all,' he says. Work on Equation began two years ago, when Cao was still an independent filmmaker with a minor hit, Trouble Makers, under his name. The film is backed by Huayi Brothers, one of the biggest entertainment groups on the mainland. Huayi has financed blockbusters such as Stephen Chow Sing-chi's Kung Fu Hustle, Feng Xiaogang's The Banquet and Assembly, as well as The Forbidden Kingdom, the Sino-US co-production starring Jackie Chan. Despite such backing, Cao remains on the periphery of the mainland's film industry. His entourage to San Sebastian has just him and Fu Jia, an independent producer who also serves as his manager-cum-publicist. Meanwhile, Cao is still on the payroll of the Beijing Film Academy. He's allowed to compress his courses into the spring semester, leaving the second half of the year for his filmmaking. Cao says he's not going to quit teaching anytime soon. He knows the perils of leaving the stability the job offers him. He spent the first 10 years after graduating from the academy writing scripts for serials and television films. His career in films only began in 1998, when he wrote an award-winning screenplay for Chung Tian Fei Pao, a 1999 film about military jet pilots. He followed that with the romantic drama Jue Dui Qing Gan in 2001. But it was with Trouble Makers that Cao finally made his name as a full-fledged director. Even then, he was to return to television work such as the soap opera 10 Months of Pregnancy in 2005 until the screenplay to Equation reached Fu, who eventually got the backing of Huayi and Hong Kong's Sundream Pictures. This strong financial support enabled Equation to bring in stars such as Zhou - whose depiction of the chain-smoking, temperamental Li Mi is astounding - and Zhang, who is now well-known for his leading role in the war epic Assembly. Cao remains refreshingly non-media-savvy. He's more at ease joking about the 'beautiful' sound of Cantonese foul words than making grand statements about his art. He says he hopes Equation can help instruct his young students about the options open to them once they start out in the mainland's film industry. 'It's like walking this tightrope between these two extremes,' he says, explaining that his film defies the binary categories of commercial and arthouse cinema. 'It's not easy - but I think I need to do this film to let a new generation of filmmakers know that there's a third way of doing a film in China. Equation could leave them with a new option.' The Equation of Love and Death, Oct 15, 7.50pm, IFC cinema, Central; Oct 18, 9.40pm, AMC cinema, Kowloon Tong, as part of the Hong Kong Asian Film Festival. It will be on general release later in the year.