The book has the names of three people on the cover, and would appear to have been written separately by all three and then shuffled together with no particular care.
The thrust of the book is in two parts, with an underlying subtext. The first part of the book is a "review" (biased from the outset) of the Cydonia artefacts. While the authors are at pains later in the book to stress they are not advocating the artefacts are of artificial origin, their writing points entirely in the opposite direction, citing government cover-ups, deliberate sabotaging of multi-million dollar missions to Mars (Mars Observer) and mounting none-to subtle character attacks on the likes of Daniel Goldin, Michael Malin of Malin Space Systems (operaters of the Mars Observer and now the Mars Global Surveyor) and even Carl Sagan. While in later chapters the authors half-heartedly withdraw some of their earlier accusations (particularly with reference to Dr. Malin), the damage has already been done, and the status and impartially of such individuals as Dr. Malin have been suitably undermined.
This is perhaps the clearest indication of what might have been strongly differing viewpoints among the authors - one perhaps strongly in favour of the Cydonia artefacts being of intelligent origin, another not being so convinced and somewhat more open-minded.
The second thrust of the book is a discussion of planet-impacting comets and asteroids, and here the book hits more of an even stride - even if the authors prefer to limit their own thinking and merely report the thoughts, conjectures and concerns of others. Where the authors do inject their own thoughts on the matter, it is largely to whitter on about Cydonia and mystical geometry once more.
And that's where the subtext to the book lay. Throughout there is a sense that the authors are really seeking to extend their (most likely misguided) belief in the construction and symbolism of the Sphinx. In The Mars Mystery, they make frequent and on-going references to their earlier work on the Sphinx, almost as if by quoting from it or referencing it, they will elevate it to respectablility by placing it in the footnotes alongside the works of Hoyle, Clube, Sagan, et al.
The book could have been a thought-provoking read. It raises interesting questions on the subject of Earth-impacting bodies. It highlights remarkable research that has been going on in the last 10 years alone in this area. Sadly, by inexorably linking such worthwhile work with trying to prove the "mystical geometry" of Cydonia, the authors do the study of Earth-crossing asteroids a vast disservice. For, as the authors themselves say, the argument over Cydona will never be settled until human go to Mars and explore Cydonia...so why the heck waste half a book in useless conjecture on that very subject?