I hadn't picked up on his mention of Iran being pertinent to his stay. I think you are onto something with your post.
As a reader of spy novels, which sort of lost their allure after the end of the Cold War but have regained popularity after 9/11, that book would serve exactly the purpose you proposed.
Exactly. Nick barely spoke Arabic, why in hell would he be hauling around a Farsi prayer book, unless it was a proof of bona fides between terror contacts?