Driven mad by mysterious rituals intended to install her as a Druid priestess and the peopleβs connection with the Earth Mother, an Irish lass finds herself in an asylum and in the clutches of criminals intent on plundering a sacred Celtic treasure that can only be found on All-Halloween.
1920 - Hooded Celtic tribespeople huddle around a stone altar in a sea cave on the Welsh coast. Tessa Wiggins watches Ganna, her Druid priestess guide, drink a deadly potion. βMy spirit passes unto you,β Ganna says, moments before a crazed witch-hunter and a band of thugs attack. Gannaβs protector, Maeve, kills the witch-hunter and flees. As the brutes close in, Maeve demands a warriorβs death, and Tessa holds the blade that Maeve runs onto.
This story begins eight months later, as Tessa works as a housekeeper at Ceridwen Manor while Gannaβs spirit prepares her to become the last Druid priestess of the Iceni tribe. Arcane rituals, sacred mushrooms, and guilt about Maeveβs death are haunting Tessa. Her lover Clark tries to help, but his efforts are rebuffed. At the same time, the legacy masterwork of her childhood friend, Sherlock Holmes, is stolen. Holmes traces the thief to Hellingford Asylum, and he asks Tessa, who was one of his irregular army thirty years ago, to go undercover inside.
Tessa commits herself and soon discovers Hellingford is a front for a notorious band of women thieves and a blackmail enterprise facilitated by a bizarre therapy. Tessa encounters Beara, an elder from her tribe, and learns that gas therapy is used to have her reveal the location of a hallowed Celtic treasure. Tessa is subjected to the same treatment, and after an intense therapy session, locks the wheelchair-bound psychiatrist in his own contraption. When he turns up dead, Tessa tries to escape with the help of a patient. But lunatics make poor friends, and Tessa is caught. In the aftermath, she learns the stolen manuscript is a scheme to lure Holmes to his death.