This book gives the reader a very good undertanding of the mystery. It is unknown whether Mallory and Irvine got to the top of Everest or not, and this book covers a good variety of theories that could have happened.
A fair bit of the book concentrates on Mallory as a person, it doesn't only talk of the mystery, which, in my opinion is a good thing. Trying to get an understanding of him helps determine what he may have done at the second step under a blanket of clouds, so as unrelated to the mystery it might seem to talk of his background, later on in the book it becomes apparent.
Do not expect an answer to the mystery at the end. Reading this book helps one create their own oppinion of the mystery, whether it be that they didn't make it, they did, or no further opinion. Rightly so, as the chances are no one will ever know for certain.
In conclusion, the book is well written, exciting, interesting and factual. Its also a must read for anyone interested in the mystery, I would highly recommend it even to people who say they aren't.