If you’re walking around Charlotte Square Gardens and need a double take towards a pair of 70-year-old women who look almost exactly the same, strong chances are it’s Helen and Morna Mulgray. The former teachers who have never been married but have lived with one another pretty much all their lives are a unique literary pairing. They unsuccessfully attempted to write romantic novels back in the 1980s before realising that crime fiction was their forte. Once they settled into their chosen genre, they knocked out a debut entitled No Suspicious Circumstances which was published in 2007 and then followed by Under Suspicion. Both books introduced their heroine, the customs and excise investigator DJ Smith, and her inscrutable sniffer Persian cat, Gorgonzola.

A third book, Suspects All, is in the bag and number four is being worked on. Long-term, they don’t see themselves ever doing a Rankin or Rowling and cutting off from their most famous creation. ‘Gorgonzola will never die and DJ Smith will never age,’ insists Morna before Helen chips in: ‘People make mistakes ageing their characters so that you get the stage where they have to retire, like Rebus.’ The pair do gentle crime where a skewer is the most gruesome instrument ever wielded in the course of a Mulgrays-inspired demise. While they may share a city with Rankin and Irvine Welsh, their work is closer in spirit to Alexander McCall Smith and their co-festival act, Alanna Knight. ‘We write cosy crime,’ insists Morna. ‘We don’t dwell on the violence, so you can imagine as much as you want.’

23 Aug 2009 (with Alanna Knight), 6.45pm, £9 (£7).