This book is an admirable, if somewhat diffuse, introduction to the subject of Celtic Christianity. However, the reader has to realize that when Mr. Mackey refers to "Celtic Christianity" he means the term in a generic sense, i.e., Christianity as it has been, and currently is, practiced in areas inhabited by people of Celtic ancestry.
As a result, this is not a book about subliminal Druidic influences, nor is it a book about prayer and praise in the tradition of Patrick, Brigid and Columba. What it is is a collection of essays on a variety of topics, which gives the book a rather scattered approach that some readers (including readers like myself) may find undesirable. However, the information contained in the book is on the whole quite interesting and illuminating. St. Patrick does, of course, figure in the book, most prominently in the first two essays on his autobiography and the lorica. There is also a very complete treatment of the Culdee communities in a later essay.
The rest of the essays tend to take us far away from what is usually associated with "Celtic Christianity" nowadays. There are essays on the Reformation in Scotland, and the Methodist movement in Wales. There is an essay on James Joyce and the whole modernist movement in Irish literature from the religious viewpoint, material on modern poetry in Irish, and a particularly interesting essay comparing the work of Douglas Hyde and Alexander Carmichael in collecting religious poetry in Ireland and Scotland in the nineteenth century.
In general, the book is an interesting read, and I recommend it for the serious historian of Celtic culture in the varieties it has evolved over the last 1500 years. Particularly recommended to those who prefer the reasoned academic approach over the murky Celtic twilight mists found in so much literature in this genre.