Arriving at a secluded ProSyntrex facility situated deep in the English countryside, seven strangers are carefully briefed on the nature of a drug trial they have each agreed to participate in: a routine, double-blind experiment run by Dr. Mansell (Chris Larkin) that aims to study the effects of Pro-9 on human subjects.

As Adam (Aneurin Barnard), Joni (Alex Reid), Jed (Oliver Coleman), Katie (Nia Roberts), Morty (Steve Evets), Carmen (Skye Lourie) and Arif (Amit Shah) receive their first round of injections, however, they soon find themselves reacting to the drug in unexpected and drastic ways. Trapped, alone and slaves to the chemicals now coursing through their veins, the guinea pigs might not survive the night, let alone the study’s fortnight-long duration.

In festivals often packed to the highest brows with pretence, pedigree and Philippine New Wave, sometimes it’s nice to kick back with a schlocky British horror movie aiming to do little more than entertain. An assured début from award-winning shorts director Ian Clark, Guinea Pigs is one of the most engaging and enjoyable movies screened at Edinburgh 2012 so far.

Opening with the participants’ arrival at the remote compound, Clark quickly and efficiently introduces his characters by way of their first appointment with Dr. Mansell. In a scene reminiscent of an early Big Brother première – back when the housemates still resembled actual human beings – the characters unpack, unwind and inadvertently lay the groundwork for the numerous conflicts and character arcs that will develop across the rest of their tenure, or indeed the film’s pithy 85 minute running time. Whereas most genre efforts would take this opportunity to let the first head roll, Guinea Pigs instead takes its time, establishing a realistic, recognisable environment that in turn builds a false sense of security.

Populating Clark’s obviously researched and impeccably designed laboratory are characters that are equally relatable and similarly well-observed. Misfits‘ Alex Reid is – as always – a pleasure as self-confessed “farmer’s daughter” Jodi, contributing a nuanced and wonderfully sympathetic performance that gives viewers someone to root for right from the off, while Aneurin Bernard does well as the film’s post-graduate lead Adam, providing an entry point into the narrative and a sense of reason once things eventually come to a head. Nia Roberts and Steve Evets also impress, meanwhile, infusing personality and depth into their roles as driven journalist Katie and experienced test subject Morty, respectively.

Effectively a body horror, playing on the primal fears of medicine and sickness, Clark expertly ramps up tension with a series of tight close-ups and measured, lingering cuts that hint at an ever-present spectre that seems always to be lurking just around the corner. Even as night falls and the blood finally starts to flow, however, the director keeps a tight hold of his characters, using each development or individual trauma to reveal something new about our makeshift ensemble of Katie-dubbed last resorters. With chilling sound-effects and suggestive cinematography keeping audiences on the very edge of their seats, the script is able to touch on topics such as ethics and human rights without ever detracting from the overall atmosphere of suspense.

Where Guinea Pigs ultimately falls down is in its disappointingly lacklustre finale. After a confident and effective build up, Clark can’t seem to bring his various plot strands together in a satisfying manner, exiling one character in particular and robbing many others of a fitting farewell. Worse, the foundations for a memorable conclusion are clearly there, evident between the lines but sadly under-represented in the script itself. Where a last-minute reveal should have provided a devastating and gut-wrenching climax, the ramifications of the subjects’ movie-long plight are instead skimmed over with a few pre-credit title cards that don’t provide the satisfaction that the audience or the characters really deserve.

With its simple premise, strong script and stronger cast, Guinea Pigs could have been something truly special. As it is, the film is let down by a weak finale that detracts from the overall experience, causing more frustration than fulfilment. Even with its failings, however, Guinea Pigs is still personally my favourite film of the festival so far, encouraging me to watch Clark’s career with interest and the highest expectations. I recommend that you do too.