Bloodroot by Cynthia Riggs

It's just another day at the dentist's office for Victoria Trumbull when fellow patient, wealthy Mrs. Wilmington, dies. It's an unfortunate, though seemingly not murderous incident, but the receptionist is hysterical, so one of the dental assistants offers to drive her home. But after making a quick pit stop, he finds her body floating in the harbor.
With the police shorthanded due to an upcoming presidential visit, it's up to Victoria to take on the case. As she wrestles with her ex-son-in-law, a $3 million will, and a deadly dental clinic, Mrs. Trumbull discovers that nothing in the case is quite what it seems.
Bloodroot is the latest in Cynthia Riggs' longstanding Martha's Vineyard mystery series, filled with delightful characters and charming descriptions of the beautiful island.