A self-assembly Swedish crime thriller is how Inspector Norse – the latest piece of deceptively casual nonsense from LipService – subtitles itself. Maggie Fox and Sue Ryding take television's current fascination with Scandinavian crime novels and series (not to mention a certain detective's taste in knitwear and the seemingly ubiquitous craze for flat-pack furnishings) and fashion them into an evening which has some very willing audience participation as well as constant gales of laughter.

There's an engaging use of puppetry and those two-dimensional landscapes and interior scenes common to folk art the world over. What at first sight appears to be a cheap edition of a book, several times price-reduced, opens to reveal the main locations in sequence as a woman detective muses on her calling (Ryding). She is much given to introspection and constantly bedevilled by phone-calls at the least appropriate moments in connexion with a new sweater currently in construction on her mother's knitting needles.

It transpires that there is a mystery about a former famous pop group quartet which has broken up after the inevitable bickering over money, fans' preferences and creativity versus stage-craft. This takes Norse and her sidekick Erik (Fox) on a mountainous journey (cue a wholesale massacre of furry wildlife as the police car screeches its speed-limit-breaking way to where singer Freya lives). Fox has great fun with this latter-day Garbo while Ryding has a series of fast wig and headpiece changes as other members of the collapsed group.

Projected video links several scenes, not to mention introducing us to all the people who have knitted props (look out for the spanner). A hard-working stage manager called Rob has meantime planted a cut-out plywood tree whose bare branches will be hung with woolly leaves during the interval (well, I did say that this was a participatory show). But don't be fooled by the apparently vague amateurishness of the introduction. This is a well-thought out, split-second timed romp of thorough-going professionalism.