Subject/verb agreement

I have a question concerning singular or plural in the following situation:
The sentense is: None of the author's books (is/are) currently in print.
I need to know which of none or books is the subject of the verb (is or are)?

[Tdol]

You'll see both being used- purists tend to use the singualr form with 'none', but to many the plural sounds more natural as it's next door to the word 'books'.