Generally, I don’t like knowing a film has a sting in its tail before I see it. So when we were asked before the screening of Aaron Kwok’s new serial killer thriller, Murderer, not to give away the film’s ‘shocking twist ending’, I knew I was destined to spend the next two hours trying to guess what the twist was going to be. Now, fear not, I am not about to reveal what happens – not because it is unpredictable, revelatory or will ruin your enjoyment of the film, but because it is jaw-droppingly dreadful. It is the kind of ending that only confirms that the majority of Hong Kong films begin production without a completed script. It is impossible to accept that anybody would have financed this project had they read beyond page 50 and I can only assume that when the financiers handed over their cash, such a page number did not yet exist.

But let’s start at the beginning. Chief Inspector Ling (Aaron Kwok) is discovered unconscious at a crime scene where a fellow cop, Tai (Chen Kuan Tai), has been savagely wounded. When Ling awakens in hospital he can remember nothing of the events leading up to the attack. It appears they were assaulted by a serial killer they had been tracking, who had used an electric drill to drain the blood from two other victims. Although Tai is still alive, his body is riddled with holes similar to the other victims.

Almost immediately the evidence points to Ling as the prime suspect. Eyewitnesses claim nobody else was seen entering the apartment block where the officers were attacked. The two previous murders took place close to Ling’s home on his days off, when he is unable to account for his whereabouts. Apart from his wife Hazel (Chang Chun Ning) and adopted son Sonny, only fellow detective Ghost (Cheung Siu Fai) stands by Ling, while the rest of the squad, which includes Chin Kar Lok and Wong You Nam, grow ever more suspicious. The media are also quick to point the finger at him, jeopardising his imminent promotion to superintendent.

It is easy to forgive the slightly uneven pace and tone in the first act, as the story seems to be building towards something genuinely exciting and potentially gruesome. First-time director Roy Chow clearly has a flair for directing horror and delivers some top drawer gross-out moments. However, after an intriguing and generally well-executed set-up, the filmmakers can’t decide where they want to go next and who eventually to point the finger at. With a flurry of flashbacks, recollections and snatches of dialogue, Chow heavy-handedly ensures his audience doesn’t miss anything of relevance. In the exposition, characters also repeatedly stop what they are doing to recite entire pages of back-story.

Where the shocks, scares and suspense buoyed up any directorial rough edges early on in the film, they cannot save Murderer from spectacularly diving into absurdity in act three. Christine To’s script clearly believes itself to be infinitely cleverer than it is as Aaron Kwok shouts, wails and twitches when not gazing ponderously out over the ocean and, even with the worn-down edginess of a man clearly in need of more sleep, he is never wholly convincing. After his double awards win with Divergence and After This Our Exile, Kwok is being taken very seriously as an actor, but Murderer may prove to be a costly misstep.

Elsewhere in the cast, Chin Kar Lok is criminally under-used as a fellow cop, while Josie Ho is handed the nothing role of Ling’s younger sister. Ling’s wife, Hazel, played by Taiwanese actress Chang Chun Ning, inexplicably speaks Mandarin while nobody else does, in a phenomenon becoming increasingly popular in Hong Kong films as the drought of decent local talent continues apace. She stands around looking pretty and worried, but little else is asked of her. Cheung Siu Fai lands the only other worthwhile role as Ghost, Ling’s partner, but, as with the rest of the supporting characters, the part is under-developed and the actor struggles to find more than one dimension.

The fact that Murderer is so unsatisfying is more distressing than disappointing. I cannot believe anybody involved with the production was genuinely happy with the film’s final act and yet everyone gives it their all, right to the bitter end. The twist is so audaciously bad that it actually makes the film worthy of recommendation, as it really needs to be seen to be believed. And it all began so promisingly too. Right from the opening scene the film is shocking, gruesome and engaging – so much so in fact, that the two teenage girls sitting next to me walked out after half an hour complaining it was too scary for them. In hindsight I might have been better off following them. James Marsh