Kelley Armstrong

Mallory Mitchell and Dr. Duncan Gray take a break from investigating murder to find the most famous dog in Victorian Scotland. A year ago, twenty-first-century detective Mallory found herself in 1869 Edinburgh, in the body of Catriona Mitchell, a housemaid working for Dr. Duncan Gray, pioneer in forensic science. Shortly after she arrived, she made the unfortunate acquaintance of Catriona's former criminal mentor, Davina, an entanglement that nearly got Mallory killed.
Now she's about to meet Davina again. Greyfriars Bobby has disappeared. The little terrier is already a legend, and Davina has made a tidy living showing him off on graveyard tours.while picking the pockets of her guests. When the elderly dog vanishes, Davina calls in a favor from her old student. Mallory agrees to help find Bobby in return for the one thing she's been unable to get from Davina-the mysterious Catriona's life story.
Note this is not a full-length novel. It's a novella set after Death at a Highland Wedding.