Director Mark Losey's splendidly nightmarish debut is a disturbing speculation on what might happen if the sort of man who wore a tie at weekends met a tattooed Scouse fugitive.
Alex MacQueen - The Thick of It's oily politico Julius Nicholson - plays Roy Tunt, an obsessive birdwatcher for whom everything must be just so - from the position of his notebook to the cut of his chicken-spread sandwiches.
Settling down for a day's birdwatching at a ramshackle hide on the Suffolk mudlflats, he's hoping to spot the rare sociable plover...and tick off the final feathered friend in his exhaustive list of British birds.
However, his solitary ornithological idyll is shattered when in blunders Dave John (Campbell), a whisky-swigging Scouser with a tense disposition that suggests all may not be right.
Initially regarding one another warily - Roy upbraids him for not following the Queen's English ("it's reasonably accessible") - the two eventually settle down to an uneasy companionship (they both enjoy a love of power tools).
Sharing sarnies...and then private hopes and fears, the two - one an obsessive-compulsive soon-to-be divorcee and the other a tattooed loner with a liking for drum'n'bass - discover they have more in common than first thought.
Losey - who has a background in award-winning ad campaigns - has come up with a beguiling thriller which draws its considerably grisly strength from a first class script by onetime Teletubbies narrator Tim Whitnall.
MacQueen is pitch perfect as Roy, the cardiganed twitcher whose clipped, articulate tones gradually reveal something much darker lurking beneath.
Filmed on practically no budget, it also looks great with the rural-industrial backdrop of the windswept mudflats supplying a suitable eerie backdrop for the menacing scenario emerging in the shed.
Losey may over-relax his tight editorial grip in the final reel...but this remains a starkly impressive first time out.
There's no place to hide.