Root of All Evil in Bloomington, MN

If Andrew Basnett were a savvy mystery reader rather than a retired professor of botany, he would know that an invitation to spend Easter weekend at the Berkshire estate of a wealthy distant relative always involves at least one murder.
This one delivers a death threat, an imminent disinheritance, a theft, and two corpses—good thing the quiet professor is around to suss out the family's secrets.