Nine-year-old Tiffany Aching thinks her Granny Aching – a wise shepherd – might have been a witch, but now Granny Aching is dead and it’s up to Tiffany to work it all out when strange things begin happening: a fairy-tale monster in the stream, a headless horseman and, strangest of all, the tiny blue men in kilts, the Wee Free Men, who have come looking for the new ‘hag’. These are the Nac Mac Feegles,…