"Star Trek: Provenance of Shadows" by David George III
I decided to try this Star Trek novel based upon some of the Amazon reviews. The first of a loose trilogy, the Cruible of the title is the death of Edith Keeler in "City on the Edge of Forever". In this book, we basically see McCoy's life from that point, told in two parallel stories (one where Keeler dies, the other where she lives). Much of the second story is therefore a historical novel, as McCoy struggles to survive in depression era Earth, eventually moving south and settling in a small town. This portion of the story is the more interesting one, since the other story is basically an overview of major points of McCoy's life in the 23rd century (much of which we know).
I thought it was an ok read, though a bit long. Only for relatively hard core Star Trek fans I think.