Firstly, Digital Fortress kept me absolutely riveted, I could rarely put the damn thing down! Secondly, although I would put it on a slightly lower par than the other Dan Brown books, I still believe you should DEFINITELY read this book - its worth spending a fiver on.
Set in the top secret NSA Government agency, Susan and her fiance David are both called in seperately to help Susan's boss with an emergency. While David jets off to Spain to recover an item which in theory should be relatively easy to gain, Susan helps her employer with the more technical side of things. A former worker at the NSA has managed to come up with a code that the NSA super-computer is unable to break. Fearing that this may go to publication and subsequently lock the NSA out of communication, both Susan and David (who is slightly less aware of the implications of his task) race desperately to find the pass-key to destroy the code altogether and consequently save the NSA.
Buy it, enjoyed it immensely.