Family Secrets, Tainted Hearts

A scion of a well to-do vassal family comes to the Heroes, vexed that her grandfather never seems to die. She is ambitious, and desires the leadership of the family for herself (her father is a dullard whom she would use as a puppet). However, every time she attempts to kill her grandfather, he manages to escape death and someone else dies instead. Not that she’ll admit to murder attempts. Finally, she is frustrated enough to ask for outside help in discovering why her grandfather is still alive, couched in terms of fear and distrust of his longevity as unnatural.

–Over the course of the adventure, if the Heroes are paying attention, they will be able to uncover her own perfidy as well as that of her Grandfather.
–Her Grandfather owns a dagger that is keeping him alive; life essence can be stored in it, and so long as the dagger has been used to kill someone in the last month, the wielder can escape death once. Whenever the girl attempts to kill her grandfather, he escapes death, and immediately thereafter kills someone so as not to lose the protection it grants.
–Vassal family of the val’Ishi, perhaps?
–Ways to discover the secret: Talk to the servants, research the blade (it’s always on his person, but there are references to it in various archaic libraries).