In a genre such as horror, which focuses so much on the nervy build-up to a terrifying third-act climax, the payoff is occasionally not worth the groundwork laid prior. In the case of The Last Thing Mary Saw, a Shudder original horror written and directed by Edoardo Vitaletti, that’s unfortunately the case. For all the work it does setting up an intriguing mystery through flashbacks, it lacks the spark or conviction to make you invest in the first place.

An understated Stefanie Scott plays the eponymous Mary, the youngest of a family of religious diehards in a rural community in 1800s New York. Their family unit, headed by the unnerving matriarch (Judith Roberts) is one brimming with conservatism – and as such, she keeps her romantic relationship with their maid Eleanor (Isabelle Fuhrman) secret. When the matriarch dies and Mary is blinded, the film recounts events leading up to this tragedy, uncovering something sinister beneath.

It may sound intriguing as a premise, but The Last Thing Mary Saw simply doesn’t do enough with the ideas it ponders. Vitaletti chooses to tell the story mostly through flashback, showing us vignettes of their life prior to the matriarch’s passing. The first act in particular is very disorienting, and doesn’t put in the groundwork to properly introduce characters aside from Mary and Eleanor. It all starts off feeling sleepy, in need of a spark, with scene after disjointed scene showing the family tensely interacting without much to hold it all together. The film wants you to already be engrossed due to the mystery around the matriarch’s death and Mary’s blindness, but that simply doesn’t happen.

This first half is arguably the film’s biggest weakness, because it simply doesn’t delve too much into the horror that it is so heavily billed around. In fact, it may be fairer to label The Last Thing Mary Saw as a family drama and thriller rather than a horror, because the ultimate payoff doesn’t feel tied enough to the genre for horror fans to invest. There ultimately is something sinister and supernatural at play, something we won’t spoil here, but it’s so poorly explained that you’re left with far more questions than answers.

It’s a shame, because there are some interesting ideas at the core of The Last Thing Mary Saw. The LGBTQ+ storyline between Mary and Isabelle is something we don’t tend to see in this time period, and the way the film navigates their balance between secrecy and passion is powerful. In some ways, the real horror is how cruelly Eleanor and Mary are treated by the latter’s family and it makes subsequent events – where things get more bloody – loaded with seething.

Equally, rising star Rory Culkin puts in a scene-stealing cameo as a vagrant merchant with nefarious intentions for Eleanor. After his brilliant work in Lords of Chaos, it’s good to see him continue with an unnerving and intensely watchable performance, crafting one hell of a unlikeable bit part. Vitaletti doesn’t overuse his character, which makes the sequences involving Culkin all the more engrossing.

But overall, The Last Thing Mary Saw feels like a missed opportunity: taking an interesting time period and LGBTQ+ outlook but bogging it down in dull, disjointed storytelling and a lack of interesting payoff. It’s worth watching for Culkin’s cameo and the shocking last ten minutes, but you’ll mostly find yourself waiting for the cogs to start whirring.

★★

The Last Thing Mary Saw releases on DVD and digital on September 19, 2022.