There’s something about the quiet isolation of rural areas that brings out the worst in people. Whether embarking on a hallucinatory adventure in A Field in England or becoming embroiled in a dark family secret in The Winter Lake, the lack of human contact inspires questionable behaviours rife for the studying, something Phil Sheerin sets out to do in this slow-burn, countryside-set thriller.

Recently moved into an old farmhouse, troubled Tom (Anson Boon) and his mother, Elaine (Charlie Murphy) adjust to their new lifestyle. Having moved around a lot in recent years in the wake of his father’s death, Tom hasn’t taken a shine to many people, until he meets his neighbour, Holly (Emma Mackey) and her protective father, Ward (Michael McElhatton). Tom discovers something untoward in the nearby lake and involuntarily finds himself in the middle of a twisted, real-life fairy tale.

Location plays a crucial role in films like The Winter Lake in establishing its atmosphere. From the first frame, a completely alone Tom in a field, the Irish countryside provides something of a mystical feel to it all. The mist rolling over the fields, the grey skyline, and the only sound coming from the howling wind around him, are an early indication that an unsettled feeling awaits both Tom and the audience. Director Sheerin and his cinematographer, Ruairí O’Brien, portray the environment as almost a character of its own. Holly describes the titular lake existing above an underground river that ebbs and flows with the seasons, disappearing in summer but reappearing in winter, again alluding to the mystical, fairy tale-like aesthetic of the local area. This proves to be one of The Winter Lake’s strongest aspects, as while the human characters often come across somewhat threadbare, the general atmosphere created is particularly effective in supporting the drama on-screen.

From the picturesque (even during an Irish, rainy winter) scenery to the creaky, wooden house Tom and Elaine find themselves in, there are impressive moments of unease dotted throughout amplified by the environment. The cramped and claustrophobic design of the farmhouse piles onto the ever-present tension between mother and son, a tension that shifts from one of family troubles to one of genuine danger as a visitor begins to slowly invade their house. Lighting, too, plays a key role in boosting the tension with some quite lovely usage of silhouettes and shadows (a side profile illuminated by a kitchen window at dusk leaves a particularly strong impression) to compliment the action as best as it can.

As one of the film’s focal points, Tom and Holly’s relationship is well explored; Holly’s confidence is evidently something Tom has never experienced, and while you wouldn’t ever have matched the two together, their “I’ll talk, you listen” relationship does develop into something quite sweet. Tom has a consistent silent streak that only really breaks to tell his well-meaning mother to fuck off. He’s frequently seen silently sitting and absorbing information presented to him, unwilling to trust anyone easily, and even jumping out of a moving car to escape someone he simply doesn’t like. Tom has a darkness within him that stretches to box-cutter violence more than once during The Winter Lake, but Boon plays it all very convincingly, giving Tom a similar edge that Dane DeHaan gave to Andrew in 2012’s Chronicle. Anson Boon plays the quiet type well and convincingly explodes in frustration more than once without ever coming across as unnatural, though you may become irritated at just how quiet Tom is throughout, going several scenes at a time without uttering a single word.

Tom proves an effective foil to Holly in a film-stealing performance from Sex Education’s Emma Mackey. She has the charisma that Tom lacks, you become drawn to her every word as the film ticks along, feeling almost as protective of her as her father when you learn the dark secret at the heart of the film and how it involves her in a particularly upsetting way. Mackey draws you and Tom into her social bubble easily, though as the film develops, you do begin to question Holly’s motivations with Tom that suggest a deeper interpretation than what meets the eye; her final appearance in the film and what it means for Tom has stuck with me since the film’s conclusion. It’s a shame that Holly’s involvement in the story somewhat peters out as the film reaches its conclusion as the film is genuinely engaging with her on screen and less so when she isn’t.

It’s a shame, though, that the film is so hung up on the mystery it’s so evidently proud of. What Tom finds at the bottom of the lake is a truly upsetting discovery and it’s no wonder it occupies his every waking thought for much of his early days in Sligo, but the film’s biggest mistake is thinking the mystery is what keeps you engaged rather than the characters attached to it. Tom and Holly’s relationship develops nicely, Elaine is a trier but a drinker and finds herself struggling to keep her son under control which leads to some hard-to-watch arguments between the two, and Ward is one of the darker father figures seen in some time, played with that similar Roose Bolton-like villainous streak by the ever-reliable McElhatton. How they relate to the mystery is what makes the film tick, so when the film inevitably becomes centred entirely on it in its final act is where the film unravels and loses focus on what works so well.

As effective as the drama between the characters may be at times, their thinly drawn archetypes begin to buckle under the pressure as the film ramps up into its conclusion, abandoning any nuance developed in the first half for a more blunt approach in its final act. Ward is a particular victim to this when his face is illuminated half in light and half in darkness to illustrate his total descent into evil, while the light beaming through the door behind Tom’s mother illustrates exactly what you think it does. There is a clear understanding of film language, but its deployment is frustratingly on-the-nose that blunts the impact for which it was surely aiming.

The Winter Lake has an impressive atmosphere that is very nicely shot throughout, but the mystery that undercuts the whole thing isn’t strong enough to tie it all together at the film’s end. All its key players come out of this well, however, particularly from Emma Mackey who’s surely destined for big things with the eventually-to-be-released Death on the Nile. The Winter Lake is an effective thriller in bursts; better when it’s exploring the relationships surrounding the mystery, worse when dealing with the mystery itself.

Rating: ★★

THE WINTER LAKE is On Demand on March 9 and DVD on March 23