The young hoodlums at the centre of this satisfying shocker lose any sympathy we may have allowed when they elect to torture, of all treasures, Sylvester McCoy and Rita Tushingham. They may as well have threatened to eviscerate Paddington and Bagpuss.

Mind you, from early on we get a sense that Dr and Mrs Huggins may not be quite so harmless as they seem.

The picture begins with perky Mary (Maisie Williams) – who may or may not end up as the “final girl” – reluctantly assisting three male friends in robbing the elderly couple’s rural pile. Terry (Andrew Ellis), whose mum works for the Hugginses, has heard there is a stack of money on the property but, after a rigorous search, they are flummoxed by a safe in the basement. The gang decides to wait for the, ahem, owners to return and torture the combination out of them.

Here is where things turn fishy. Dr Huggins hands over his credit card and a grand in cash but, even when the gang threaten to cut off his wife’s finger, he won’t pass on the code for the safe. What can be in there?

That’s a neat set-up and Julius Berg’s debut feature, based on a Belgian comic, pretty much delivers on the delicious potential.

Hanging around youths who range from the amiably confused to the potentially homicidal, the film begins as a home invasion thriller and ends in Old Dark House territory. Along the way it takes in a dollop of gooey violence and efficient character development. Berg reveals strong horror chops as he cuts furiously and, in a late, bravura move, pulls the ratio from widescreen to Academy (or thereabouts) when the tension reaches its peak. There are some moments of water-treading around the 60-minute mark, but the final career through bloodied rapids will dispel all that.

Williams and her contemporaries are excellent. The senior actors do, however, steal the show. It’s lovely to see both having such a disreputably good time.