Hettie and Tilly are summoned to a mysterious tea party hosted by Tilly's long-lost great-aunts. The ancient windmill they live in is not what it seems, and very soon the mill begins to reveal its terrifying secrets of murder and betrayal. Tilly must face her familys demons as Hettie fights to unravel the tragedies of the past. Who are the hippy cats camped in the field? Why do the walls of the windmill whisper at night? And who haunts the derelict priory? Will Hettie and Tilly have the wind blown out of their sails before this baffling case is brought to a grinding conclusion?