Colouring books for adults are all the rage at the moment, but one of the problems with popularity is that the books do tend to become a bit, well, ''samey''. Once you've coloured in one peacock's tail, it's not easy to get inspiration for another and there's a limit to the number of flowers, patterns and mystical beasts which you can attach to the fridge door. We've seen all sorts of variations, such as mindfulness, but what we really want is something ''fresh'' and with a bit of something extra to get the brain cells going. Welcome ''Sherlock: The Mind Palace''.