An excellent, well-referenced, skeptical introduction to the - quite often ludicrous - world of cryptozoology, Naish' book is well-written, logically argued and impressively fair-minded and respectful.
Approaching his subject from a scientific, rather than polemical viewpoint is a real strength. During his discussion of the Patterson-Gimlin film (a fairly obvious hoax) he clearly lays out his case against Patterson as the hoaxer but, at the same time, berates those so eager to assassinate Patterson's character that they too, will blindly fall for dubious testimony that suits their own beliefs.
As a historical overview, Naish writes clearly about cryptozoology 'pioneers' like Ivan Sanderson and Bernard Heuvelmans. He patiently explains just how (and why) they got so many things wrong, too. Of course, he tackles the field's big names like the Loch Ness Monster, Bigfoot but also, lesser known supposed creatures, particularly from Africa and Australia. His global scale helps to back up his convincing central point - that cryptozoological sightings are based on myths common to all cultures and to basic mis-identifications of existing animals, whether due to honest mistakes or to blatant scams.
His chapter on alleged sea monster sightings is excellent, particularly his truly grotesque explanation of the mysterious 'globsters' that are sometimes washed up on beaches and claimed as the corpses of unknown beasts: "what seems to happen is that as a floating whale carcass decomposes, the bones drop away, leaving a ragged, rotting, lumpen mass formed of the skin and associated muscles and ligaments."
Nice.
In discussing Australia and its vast, open spaces, he notes that it's perfectly possible that ARE some small, as-yet-undiscovered creatures out there. He just doesn't think (and he gives plenty of solid reasons for this view) that elephant-sized lizards have managed to escape widespread detection.
His closing chapter 'The Changing Face of Cryptozoology' is excellent, and clear enough to read as stand-alone piece, he begins by arguing that "the primary tenet of cryptozoological literalism has failed... that myths, ethnic knowledge and eyewitness accounts pertaining to mysterious creatures provide evidence for the existence of numerous undiscovered species" but notes that, divorced from the credulous trappings of Bigfoot-hunting, "reports of many mystery creatures are still worthy of investigation. They might not always include the superstars of the field, like Bigfoot and Nessie, but they're exciting and interesting nonetheless."