The Curse of Harken Hall

From publisher blurb: Clovis Harken, Lord of Highcliff Gard has but six months to live, at least if the family curse is anything to go by. His wife, Karlina is going frantic as he has forbidden any from investigating the curse. But he has gone on a hunting trip, and Karlina has sent word to the wayside Inn asking for investigators to explore a mysterious door hidden behind a mural in the oldest part of the manor. It's easy money if it were but a simple coal store....