Helga Allowby, a self-described spinster, has been accused of sending noxious poison pen letters to the residents of her village and she wants Hetty to prove her innocence. Hoping to penetrate the mistrust that pervades the village, Hetty goes undercover as Tara Hall, a visiting painter. When Hetty turns up next on the mailing list, she suspects that Miss Allowby is guilty of bad penmanship.

Hetty gets mystical as she investigates Maurika Rome, a spiritualist suspected of using séances and blackmail to prey on the savings of the recently widowed. When Hetty goes undercover and invents a late husband she wishes to contact, she begins to wonder if Mrs. Rome isn't the real thing - until a woman claiming to be her "late husband's" illegitimate daughter shows up demanding money. Geoffrey's secret romance with Rome's daughter, Sara, threatens to undermine Hetty's carefully laid trap and nearly causes him to quit the agency.