The protagonist in this novel grows up in a loveless, dysfunctional family, but finds refuge and success in mathematics until he is "saved" by a physicist.
Since I do not read German, my knowledge of this book comes only from a brief email from Thomas Riepe who kindly wrote to bring it to my attention and Google's translations of some Webpages about it. So, my description above may not be completely correct. There are certainly some literary critics who have positive things to say about it like:
Contributed by
Google Translation of a review by physicist Harald Lesch
If you really want to immerse yourself in the madness of mathematics and how terrific it is to understand something about it, "Nagel im Himmel" is an absolute must.

It sounds to me like this is another one of many works of literature in which the field of mathematics is portrayed as if it were a psychological disorder like depression or paranoia. That is so far from how I perceive it, I suspect that I would have difficulty enjoying this book no matter how well it is written nor how much it is able to say about the mysteries of prime numbers. But, I hope that I am mistaken and that someday in the future I can update this posting to say that this is one of my favorite works of mathematical fiction. If you have had a chance to read this novel and can provide more information about the plot and especially about its portrayal of mathematics and mathematicians, please drop me an email to let me know.
(I'm curious about the title. It translates to "Nagel in Heaven" if the first word is a proper name, perhaps referring to the philosopher Thomas Nagel. Or, it could also be "Nail in Heaven".) 