This book is a piece of "literary detective work"; it seeks to find the myths and stories that inspired Tolkien in his creation of his three great works: The Hobbit, The Lord of the Rings and the Silmarillion.
The author states something of a disclaimer at the beginning though:
"In Tolkien's Ring, we will survey a vast body of myth and legend in search of Tolkien's sources. We will look at other rings and ring quests, and we will see where many elements of his epic tale were provoked into existence. However, we should never mistake Tolkien's creative process as a mere cobbling together of ancient lore. Richer and more profound through Tolkien's writing is for the ancient tradition it draws on, Tolkien's art is by no means imitation. The Lord of the Rings is a highly realized and originally conceived novel that has renewed, invigorated and finally reinvented the ring quest for the twentieth century." (page 17)
I think the author correctly identifies the primary time period and location that served as the prime inspiration for Tolkien. To use England as a benchmark, the time period runs from the end of the Roman period in England (406 AD) to the Conquest of William the Conqueror (1066 AD). The location is that is northern Europe; Scandinavia and Germany in particular.
The author also makes some interesting insights regarding metallurgy, the Iron Age, alchemy and ring-based mythology. The ring in that time period (especially in Scandinavia) was a symbol of power (e.g. Kings are "ring-givers") and it became the central symbol of the struggling pagan religions of Europe against the Christian symbol of the Cross. In many of the ring myths, the hero is always questing for a ring, which will provide him the power to rule the world, increase his physical strength, increase his wisdom or provide him with other such powers. This reflects the discovery of iron making; those who know how to make iron had a clear advantage of those who did not. Iron knowledge was thus precious and often kept secret. The knowledge to control and manipulate iron was often combined with magical/alchemical ideas; this led to the idea of the sorcerer-smith.
The Niebelungenlied (a Germanic epic) and the Volsunga Saga (Norse; unknown date. Probably within 400-1000 AD) were the prime examples of what Tolkien called the "noble northern spirit," of Germany and Scandinavia. Tolkien's tale leans more towards to German epic with its sense of morality reinforced by strong elements of Arthurian legend. The idea of a sorcerer/magician as a wandering old man with beard and hat was clearly modeled on the depiction of Odin (to draw a rough analogy; he is the Norse version of Zeus) in the Volsunga Saga.
In reading this book, there were times where I thought the author was really stretching his source material. It may be interesting to investigate the ring mythology of Tibet, but this was not exactly a significant influence on Tolkien. There were other times where the author simply summarized the myth; an entire chapter could go buy without reference to Tolkien or his works. With respect, when I buy a book on Tolkien, I expect to find analysis and discussion OF Tolkien. The author's analysis could have been improved by investigating Tolkien's life; what sagas were his favorites? Why did he like them? Did he read the sagas in the original languages (I happen to know he did, from reading one of his biographies).
The second last chapter is a synopsis of Richard Wagner's huge opera, "The Ring of Nibelung." The author makes the point that every age retells and adapts the ring myth for its own time and that this opera was written for 19th century Germany. However, if the reader has been paying attention to the previous chapters, this is simply a repeat of the previous stories with some changes.
The last chapter is a chapter of speculation on, "The Lord of the Rings." The author seeks to understand why it has become so popular and how the message of the novel can be applied to our times. Thankfully, the author includes this disclaimer:
"That is not to say that The Lord of the Rings is an allegory of our time. Tolkien rightly rejected the allegorical view as too narrow for his tale. He especially abhorred questions of the 'Are Orcs Nazis or Communists?' kind. Tolkien's purpose was both more specific and universal than that." (page 177)
My main criticism of this book is the total lack of documentation. There are no footnotes, no endnotes, and no bibliography. One wonders where the author got some of his ideas (e.g. a legend about Solomon controlling demons) and it would be helpful if the author could have recommended good translations of the relevant epics and other such information.
Reading this book was somewhat difficult for a person who is not familiar with the literature of the "noble northern spirit"; the barrage of unfamiliar names, places, spirits, Gods etc is difficult to keep track of. It is unfortunate that this literature is given almost no time in school curricula compared to the time given to the Roman and Greek mythology. Western civilization is based on Greco-Roman culture and Christianity, but that does mean the literature and culture of the so-called "Dark Ages" ought to be neglected.