Silent on the Moor by Deanna Raybourn, book three in the Lady Julia mysteries
In Grimsgrave Hall, enigmatic Nicholas Brisbane has inherited a ruined estate, replete with uncanny tenants and one unwanted houseguest: Lady Julia Grey. Despite his admonitions to stay away, Lady Julia arrives in Yorkshire to find Brisbane as remote and maddeningly attractive as ever. Cloistered together, they share the moldering house with the proud but impoverished remnants of an ancient family: the sort that keeps their bloodline pure and their secrets close.
Young widowed Lady Julia Grey and her sometime friend and partner Nicholas Brisbane are back for a third installment, this one set in Yorkshire. I love this series and these characters in general, and this third installment had the added delight of all the trappings of a traditional gothic - a decaying manor, a mysterious aristocratic family, secrets and murder and various mayhem.
Highly recommended, but start with the first book in the series, Silent in the Grave - the mysteries mostly stand alone in this series, but trust me, you want to see the relationships develop.