When Insidious Chapter 2 concluded back in 2013, paranormal investigators Specs (Leigh Whannell) and Tucker (Angus Sampson) decided to continue working despite the death of their associate and leader Elise Rainier (Lin Shaye). In the film’s final moments, the audience sees that Elise is still with them as a spirit, and that ending promises a fascinating new direction for the series. It was such a clever idea.

Insidious Chapter 3, released two years later in 2015, avoids that set-up almost entirely. Instead it focuses on a haunted apartment and a teenage girl, and shows how Elise, Specs, and Tucker first came to work together. It is not just that it is a prequel – it deliberately leaves the best idea of the Insidious saga on the table.

Prequels represent terrible filmmaking. While the sequel will reveal what happens to a group of characters next, the prequel simply retreads where they have been. Sequels create drama and suspense; prequels deliver trivia. As the audience, we do not need to know how Elise first met Tucker and Specs. If such detail was important, it would have featured in the original film’s screenplay. Represented here, the revealed backstory might satisfy curiosity but it does not feel engaging. The first two Insidious films were wild, unsteady creations with an unbalanced tone and a surfeit of ideas, but at least they were broadly fun. Insidious Chapter 3 wedges an ordinary supernatural thriller into the prequel format, and disappoints in the process. It has a solid build to its central plot, but it is coldly unambitious.

That central plot circles around Quinn (Stefanie Scott), a grieving teenager whose mother has died and whose father Sean (Dermot Mulroney) struggles to cope as a single parent. In her grief, she tries contacting her mother’s spirit. Whatever it is that replies from beyond the grave, it is not her mother – and it has ill intentions towards Quinn.

It is the sort of plot that fills up space comfortably, but fails to innovate or present original ideas. It is instead a framework to enable the return of three key supporting characters from the original Insidious, without actually paying off any of the events or character development of that film. It is watchable, even fitfully enjoyable, but while the first film was over-full and the second weakened by offensive story elements the third is simply dull. There is clearly potential in Insidious, but three films into the franchise nobody seems to have successfully found it.

In addition to writing and acting, Leigh Whannell also directs. It is a natural progression – novelist and filmmaker Clive Barker once remarked that all writers eventually turn to directing their own work – and Whannell succeeds in a solid and enjoyable manner. One wonders if this is why the third film exits at all: it is less of a film and more of a calling card, advertising Whannell’s talents for future producers while partner-in-crime James Wan is off supervising the ever-expanding Conjuring franchise.

This is a watchable, weakly enjoyable act of treading water.