J.L.
If you use a comma before and after a word, it means that word can be taken out.
For example....
Hiaasen's characters in his book, Hoot, establish an inspiring mood...
Hiassen's characters in his book establish an inspiring mood.....
So if the sentence sounds correct without the name of the book, but you want to add it, use a comma before and after.
This is actually one of the most difficult rules of comma usage....its gets everyone confused.
Hope this helps.
Edited..sorry I forgot to say it's used as a parenthesis for added info, not necessary unless you want it (and without it wont change the meaning of the sentence). I hope that clarifies my answer.