Between 2000 and 2001, a serial killer stalked the Iranian holy city of Mashhad. Saeed Hanaei, known as ‘The Spider’, murdered at least 16 sex workers. On his arrest he claimed that he was on a jihad against moral corruption and that God would approve of his actions, and large sections of the Iranian authorities and media agreed. Ali Abbasi‘s dramatic depiction of the case, Holy Spider, isn’t afraid to get stuck into the killer’s sticky web, and the strands of this bleak, violent, and deeply disturbing work are difficult to wash off.

Holy Spider follows Saeed (Mehdi Bajestani) around halfway through his spree. An unremarkable man with a wife and children, he’s a veteran of the Iran-Iraq war who is bitter he wasn’t ‘martyred’ during his service. This bitterness has festered into a hatred that he directs at the numerous sex workers he believes are a moral outrage in a holy city. After each kill he calls Sharifi (Arash Ashtiani), the editor of a local newspaper with information on the murder. Sharifi is aided in his investigation by freelance journalist Arezoo Rahimi (Zar Emir-Ebrahimi), who was forced to leave her previous position after refusing the advances of her editor. Realising the police aren’t overly zealous in catching this killer with whom they largely sympathise, Arezoo decides to cut directly through the Gordian knot of misogyny that binds all of Iranian society and put herself in danger to confront the Spider.

Abbasi begins the film by bearing witness to the grim final evening of Somayeh (Alice Rahimi) as she picks up various punters and fortifies herself with opium before her fateful, horrific encounter with Saeed. While obviously empathetic to Somayeh and critical of the societal conditions that forced her into such a desperate situation, the treatment of her murder – and the intimate and extended focus spent on it – tiptoes along the line of exploitation. It sets up the themes and context of the story, but also the slightly jagged tonal edge that the film retains throughout, one which adds to the oppressively grimy atmosphere that clings to the soul like napalm. This prologue also introduces us to Mashhad (actually filmed in Jordan for obvious reasons) as a dark and threatening entity in its own right. As the camera pulls away from Somayeh’s corpse to an aerial shot of the city, the inescapable conclusion is that it looks rather like a web.

While not subtle in its treatment of its themes (an early, chronologically anachronistic clip of 9/11 shows what Abbasi thinks about martyrdom), Holy Spider is incredibly nuanced in its characterisation of Saeed and Arezoo. Both are wonderfully played by Bajestani and Emir-Ebrahimi (who was also able to drawn on her own direct experience of Iranian misogyny). Saeed’s opinion of himself as an angel of vengeance is undercut by his depiction as an incompetent bungler who’s only escaped capture for so long thanks to the utter indifference of the authorities. Arezoo is a driven and courageous person, but there’s also the sense that the salvaging of her career is of at least equal priority to saving the lives of victimised women. It’s interesting that both really come to the fore in the third act, which ditches the noir thriller trappings and embraces Saeed’s adoption as a cause célèbre by large swathes of the population. Splendid support is offered here by Forouzan Jamshidnejad as Saeed’s psychotically supportive wife Fatima and Mesbah Taleb as his son Ali, a wheedling little prick who nevertheless dreams of following in his father’s footsteps and who gets the film’s grimmest punchline.

Holy Spider has been compared to both Zodiac and Memories of Murder, but both of these films highlight the investigative aspect, and Abbasi isn’t as interested in the procedural element of the story. This has ben interpreted as a narrative flaw by many, perhaps by those disappointed that it isn’t the cat-and-mouse thriller they were expecting. The fim is actually more of a dual character study, and a deeply uncomfortable one. In its willingness to get into the granular details of Saeed’s life, Holy Spider is more akin to Henry: Portrait of a Serial Killer or The Vanishing. You could even stretch its lineage as far back as Fritz Lang‘s M, and it’s this willingness to examine the humanity of a murderer rather than write him off as a monster that makes it so disturbing. That such a man could be celebrated for his actions provokes an almost emetic response. It might stretch itself thin thematically as it thunders home the same points repeatedly, and its easy to see why the intense and brutal depiction of the murders have led to accusations of more exploitative sensibilities, but – especially given recent events in Iran – Holy Spider is an effective, relevant, and unflinchingly grubby thriller.

In selected cinemas nationwide now