Greer defines monsters as "beings that cannot exist, according to currently accepted scientific theories about the way the universe works, but which are routinely encountered by credible witnesses and described in traditional folklore". The major portion of the book extracts the common threads from world-wide folklore and modern day sightings of vampires, ghosts, werewolves, creatures of faery, mermaids, dragons, spirits, angels and demons, while dispelling modern TV myths. Although cultures vary in their interpretation of what monsters are, there is surprising agreement about what they do. This suggests that there are common phenomena that have been subject to different interpretations.

I was particularly attracted to the book because of this well-structured and systematic distillation of the evidence, old and new. It is written in a sensible style that gives one a great deal of confidence in the author. However, there is much more that is of interest, and different audiences will take different things from the rest of the book. For the complete newcomer to the field, there is an introduction containing a cogently argued defence of the idea that evidence shouldn't be discarded just because it doesn't fit our current theoretical models. However, the main thrust of the book is as a guide for psychical researchers, ghost hunters and other investigators of spontaneous anomalies. It contains some extremely practical information about e.g. equipment to take, questions to ask and how to ask them, how to detect hoaxes and how to do research. This should be required reading for any person involved in field work of this kind.

The monster catalogue itself contains two parallel threads. Besides describing reported monster behaviour and the development of associated folklore, the author also provides an interpretation, based on Western magical philosophy, of what the monsters are and how to deal with them. Fortunately, he keeps these threads fairly separate, so that one can extract a lot of useful information about monster sightings, even if one chooses to ignore the magical perspective. That said, the framework that he presents is internally consistent and seems to be an interesting way of analysing monster lore. The notions that he draws on could also be interpreted in terms of other cultural philosophies, and students of e.g. eastern mysticism or holistic medicine will find parallels in their own philosophy to the concepts used here.

While reading this book, I was consistently impressed by the author's clear mind, down-to-earth approach and considerate nature. While each element of it may be covered in more detail in other books, this is an extremely useful synthesis of many ideas. I found a lot to think about in it, and I recommend it highly.