Belladonna

Nineteen-year-old orphan Signa Farrow confronts Death--and her own deathly powers--when she investigates the mysterious murder of a relative at the Thorn Grove estate.
Signa has been raised by a string of guardians, each more interested in her wealth than her well-being-- and each meeting an untimely end. Her remaining relatives are the Hawthornes, an eccentric family living at Thorn Grove, an estate both glittering and gloomy. Its patriarch mourns his late wife through wild parties, while his son grapples for control of the family's waning reputation and his daughter suffers from a mysterious illness. When their mother's restless spirit appears claiming she was poisoned, Signa realizes that the family she depends on could be in grave danger. Her best chance of uncovering the murderer is an alliance with Death himself, a fascinating, dangerous shadow who has never been far from her side. -- adapted from jacket