The residents of the in-grown town of Royston Vasey have a problem: the end of their world is approaching because their creators (Gatiss, Pemberton, Shearsmith and Sheen, playing Dyson) have stopped writing about them. So three of the townsfolk--mad butcher Hilary Briss (Gatiss), suggestive German Herr Lipp (Pemberton) and annoyed businessman Geoff Tipps (Shearsmith)--head through a portal to confront the League in their London office. But to save Royston Vasey, they must also cope with characters from the writers' new project, a 17th century demonic thriller.

Sounds complicated, but it's not too difficult to follow; it plays like a wacky time-travel romp between parallel universes. And while the plot is deeply self-absorbed, the dialog is extremely clever, with humour that combines astute satire, outrageous puns, gallows wit and out-of-control absurdity. It's Monty Python meets the Hammer House of Horror ... but with the storyline from that awful S Club movie.

Intriguingly, the film is probably more enjoyable for people (like me) who never got into the TV series, simply because the filmmakers focus on only three Royston Vasey residents, giving them involving character arcs. The best strand is Herr Lipp pretending to be Pemberton, getting a taste for life with his wife (Woof) and kids. But all of the characters are so well-realised that they really leap off the screen. And the starry cameos and side roles are extremely well-cast.

As it progresses, the film gets increasingly crazed, keeping us laughing through the sheer carnage. Effects become outrageous (including a Harryhausen-inspired climactic homunculus) as we head to the big face-off between people from the story's three realities, with fictional characters demanding that their creators write new scenes for them. There's the germ a strong idea here (see most of Charlie Kaufman's work), but the filmmakers are happy to just keep it deeply, gruesomely silly.