Salvation Boulevard is more demanding stuff: it's a mystery about a private investigator hired to find the killer of a college professor that becomes an exploration of religious faith when it turns out that the professor was an atheist, the P.I. is a born-again Christian, the main suspect is a Muslim student, and the defense attorney is a Jew. Sounds a bit contrived, but I suspect we're missing some data. The movie's executive producer is quoted as saying that the book "uses a mystery to examine the religious process, the mega-churches and how they manipulate minds."
The novel comes out in September, and no schedule's set for the production of the film. In the meantime, go find Joshua on DVD!