The book itself is quite well written (one of the very few books I managed to almost finish in one sitting) and gives some interesting accounts of what went into the proof. It also tells stories about ancient Greek mathematics, few 17th and 18th century mathematicians and of course Andrew Wiles and his contemporaries. All this is intended for non-mathematical audience though. If you want to look at look at the mathematics Fermat's Last Theorem developed (i.e. the wrong proofs developed) read Paulo Ribenboim's "Fermat's Last Theorem for amateurs" or this link which also includes some ingredients of Wiles' proof.
It is interesting to realize the kind of gamble Wiles played. He set about proving the theorem in 1986 when it was realized that FLT would be implied by the Taniyama-Shimura conjecture (this was proved in Berkeley :-)). For the next seven years he worked in the attic of his home working with different techniques to prove the conjecture and announced a proof at Cambridge in 1993. It was later found to have a flaw which he corrected in 1994. Devoting a large part of his professional life to a single problem and working in secret all the time does require not only tenacity but also an amazing amount of self-confidence.
I wonder why although we say Indians are good mathematically, we hardly see examples of any great mathematics being done in India (ok - with the exception of the Primality testing algorithm). Is our education system geared towards a large number of "reasonably good" people rather than a few really good ones? Or are we afraid of the risks in focussing on one single thing and want to go for the low-hanging fruit? Ok.. enough of blabbering - go read the book!