Twelve-year-old Annie is invited to Hexer Hall to work as a servant for the mysterious Lady Hexer. Carvings of snakes are everywhere and when Annie touches one, she travels back in time to when the Hall was a leper hospital, run by a sinister doctor with a collection of terrifying serpents. Annie never wants to return, but Lady Hexer demands she finds a way to steal the doctor's book of magical cures. She promises it will rid the world of disease, including tuberculosis, which killed Annie's mother. Summoning all her courage, Annie travels back in time again...