Showing Robber's Wine by Ellen Hart

The first of the dead is wealthy Belle Dumont, who vanished from her home in the northern Minnesota woods only hours before she was to reveal startling news to her three grown children. The kids and Belle's partner deny any knowledge of this mysterious bombshell, but amateur sleuth Jane Lawless, Belle's old friend, suspects this charming family of being less than forthright. In fact, she suspect cold-hearted murder.