The Poisoner's Ring - Kelley Armstrong

Edinburgh, 1869: Modern-day homicide detective Mallory Atkinson is adjusting to her new life in Victorian Scotland. Her employers know she’s not housemaid Catriona Mitchell―even though Mallory is in Catriona’s body―and Mallory is now officially an undertaker’s assistant. Dr. Duncan Gray moonlights as a medical examiner, and their latest case hits close to home. Men are dropping dead from a powerful poison, and all signs point to the grieving widows… the latest of which is Gray’s oldest sister. Poison is said to be a woman’s weapon, though Mallory has to wonder if it’s as simple as that. But she must tread carefully. Every move the household makes is being watched, and who knows where the investigation will lead.