There are 7 books in the Diana Tregarde Investigation series.
The Diana Tregarde Investigation series does not have a new book coming out soon. The latest book, Trio of Sorcery (Book 4), was published in November 2010.
The first book in the Diana Tregarde Investigation series, Burning Water, was published in February 1989.
The Diana Tregarde Investigation series primarily falls into the General Fiction genre.