Steven Moffat, who created sitcoms such as Coupling but is now perhaps best known as the showrunner on Doctor Who, and multi award-winning Discworld novelist Sir Terry Pratchett (pictured) have both agreed to take part in Ad-Lib this week.
Pratchett was diagnosed with Alzheimer's disease in 2007 but continues to make public appearances and his latest book, The Long War, co-written with Stephen Baxter, was released earlier this year.
AdLib is described as "a live entertainment show concept which explores and celebrates 'spontaneous genius'", but the show description does not elaborate further on how the format works.
Stuart Snaith says: "AdLib promises an hour of spontaneous and unexpected conversation from some of Britain's sharpest, funniest and most creative brains. This initial series of five special shows, each with intriguing combinations of stars, will celebrate their talent and explore their Scottish links."
Ad-Lib is at 10.30pm at The Assembly Hall from 21st August to 25th August. The full guest line-up is listed below...