As I always have with Tess Gerritsen's novels, I thoroughly enjoyed I Know A Secret. There are almost as many stand alone books as there are in the 'Rizzoli & Isles' series.
The plot is fascinating and horrifying at the same time, ESPECIALLY as it relates to the deaths of Catholic saints. Yowser!
Gerritsen's writing is crisp and she doesn't bog the plot down with unnecessary verbiage. I feel she 'closed the book' on one story line that threaded through the series, reinvigorated some others and left an opening to revisit one sociopath we meet in I Know A Secret.
I do think you can read this as a stand alone book, but I think it is so much more enjoyable knowing all the back stories.
What I really appreciate about Tess Gerritsen as an author is her brilliance that stems from her life outside being an author. I think both Linda Fairstein and Kathy Reichs, share equally impressive resumes with her that make their books stand out.
I am so glad I have never watched the TV series I can think of exactly ONE author whose books translated well to the screen (Larry McMurtry), so I make it a point to avoid movies and shows by authors I like. It drives my hubby crazy.