To date, the Insidious franchise has been largely composed of prequels to the original film, all of which serve to establish paranormal investigator Elise Rainier, played by Lin Shaye, as the real star of the series. The closer we get to the events of the first Insidious, the more the films elaborate Elise’s past, as if to compensate for the fact that she died at the end of the original, meaning the franchise lost its best character at the very moment it started to conceive of itself in serial terms. Chapter 2 tried to address that paradox by offering a sequel and prequel in one, using the events that occurred immediately after the ending of the first film to pivot back in time and centre Elise’s narrative. While the result was quite clunky, a more elegant version of that same impulse occurs in The Last Key, which focuses on Elise’s final months and days before she gets the phone call from the couple in the first film, but by way of a case that forces her to confront her childhood, and the origins of her peculiar paranormal proclivities.

Chapter 3 ended with Elise joining forces with ghost hunting team Specs and Tucker, played by Leigh Whannell and Angus Sampson, the three heading off into the sunset for what felt like the start of a supernatural workplace sitcom. That sense of camaraderie is still present in The Last Key, but it’s muted by the main case, which reconnects Elise with her deepest trauma. For the film quickly moves from the anonymous suburbia of the first three releases to Five Keys, New Mexico, where Elise grew up as the daughter of a prison warden. In retrospect, we see her cower in fear as her father Christian, played by Bruce Davison, holds tyrannical sway over the family. In the present, the current owner of the house, Ted Gazra, played by Kirk Acevedo, calls on the Spectral Sightlines team to look into a possible haunting.

By expanding the geographical ambit of the series, The Last Key also expands the dimensions of the Further, the invisible world-within-our-world that generates the supernatural element of the franchise. Here, we meet another entity from the Further, Key Face, and the film focuses almost exclusively on him (or it), meaning that The Last Key plays more like a creature feature than any of its precedessors. In that sense, the fourth film echoes that moment in classic horror franchises, at about the fourth or fifth instalment, when new antagonists start to emerge, often at an oblique or tangential remove from the original mythology. And Key Face is one of the most terrifying emissaries yet from the Further, and from the Insidious franchise – a condensation of its endlessly porous thresholds, and its constant involutions of inside and outside, into a single creature. For Key Face displaces the comforts of doors, barriers and locks by treating its victims as doors, and then “locking” them by inserting a key-finger into their throat. Across the first three films, the series evokes the peculiar suffocation – part claustrophobia, part agoraphobia – that comes with a digital horror milieu in which the physical thresholds of analog horror simply don’t apply. That fear of domestic and bodily porosity finds its consummate expression in Key Face, who by “locking” his victims’ throats, both constricts their air passages, and opens them up to the ambient air in traumatic tandem.

With Key Face also comes a broader sense of horror and suspense. Spectral Sightlines has more supernatural paraphernalia this time around, while the series also reflects the true crime boom with an innovative twist – namely, that both Elise’s father, and the current inhabitant of her home, are actual serial killers, above and beyond the operation and influence of the Further. To be fair, there is some suggestion that the Further induced these two men to imprison and assault women, but their pathologies are never entirely attributed to magical causes, leaving Elise to wonder whether her father was inherently evil, or whether  he was just another symptom of the Further’s tendrils. This produces a unique tone for the series, further complicated by a recourse to more traditional suspense (as befits a film that contains actual serial killers) as well as a tacit concession that Whannell and Sampson are flat actors, and completely out of place, which is played to a comic and even surreal effect here.

On top of all this, the franchise continues to make cold light its driving aesthetic principle. The first three films are notable for their daylight horror, and while The Last Key seems to contain more night scenes than all of them combined, it’s perpetually ruptured by electrical motifs. We learn that Elise’s mother was hung by Key Face from electric wire, waves of static ripple through the mise-en-scene whenever Elise touches her keys, Elise meets a critical character while unveiling voice activated lights, and her house (and memory) is continually over-illuminated by glitches trickling down from the electric chair in the adjoining prison. It’s a safe bet, then, that the upcoming fifth film, Insidious: Fear the Dark, will continue this cold daylight horror in some form, even by embedding it in the depths of the night, as occurs with The Last Key, and with Shaye in the casting list, in what has been otherwise marketed as a direct sequel to Chapter 2, it’s clear the franchise is going to have to reinvent its core vision in other ways.