Robber’s Wine by Ellen Hart

When Minneapolis amateur sleuth Jane Lawless and her saucy sidekick Cordelia Thorn set out for the sleepy shores of Pokegama Lake to escape the urban swelter and visit with their old friend Anne Dumont, hope for a little R & R quickly heads south. Hot weather incites even hotter tempers as a mysterious death in the town's most prominent family triggers a bizarre series of events that sends the Dumont clan into a dizzying spiral of deadly intrigue.