An almighty twist and a demented finale rescue the Shaun of the Dead actor’s cartoonish homage to folk horrors – but co-star Aisling Bea deserves better

The trouble with Nick Frost’s knowingly cartoonish and silly comedy paying homage to folk horrors such as The Wicker Man and Midsommar is that Frost has done this kind of movie before, and better. His hugely enjoyable collaborations with Simon Pegg and Edgar Wright, Shaun of the Dead and The World’s End, had a perfect command of comedy horror. The tone here feels less good natured, more self-congratulatory, the comedy not quite so light on its feet. Though it comes into its own with a cheerfully gruesome gorefest in the last half-hour.

Frost writes and stars alongside Aisling Bea (who really does deserve a better horror film). They play Richard and Susan Smith, an ordinary-seeming middle-aged couple with the irritating habit of calling each other “mummy” and “daddy”. The Smiths have dragged their bickering grownup kids Sam (Sebastian Croft) and Jessie (Maisie Ayres) on holiday to a fictional Swedish island to watch the Karantän festival. Every year locals stage an eight-hour re-enactment celebrating a grisly episode of early 19th-century history when their ancestors turned cannibalistic and chomped four British soldiers who’d starved the island.