The Poison Garden by A.J. Banner is a psychological thriller by a real master of this genre.  Principally set on a drippy, slightly spooky island off Seattle it reeks of tension. Elise, newly married to Kieran, the island doctor, has her world turned upside down early on. She is the proprietor of an herbal apothecary and knowledgeable about all kinds of nefarious plant life, a talent she inherited from her mother. As evil draws closer she has to use every advantage to stay ahead of those who seem to wish her ill. There are other interesting characters to round out the cast, and the plot speeds along taking lots of unexpected twists. This is lots of fun!