The basic premise is interesting enough. Lucy Merritt returns to the Himalayan country of Nhala, the sight of her parents' deaths, under the guise of restoring a manuscript. Actually there at the request of her CIA godfather, she provides a cover story for her "fiance," who is actually Army Captain Mike Shafer. He's on a mission to find an important USB drive, containing information about a frightening virus.
Despite being disappointed in the book personally, I'll note the author thinks this might be her best book to date, as indicated in her blog here.
My overall personal rating of Darkness at Dawn is a C+.