Totally misleading title - should be done under the Trade Descriptions Act really. Only gets to answer the claim of the title in the second to last chapter! The topic definitely deserves a proper going through as Cahill admits in the footnotes - the only study on Irish missionaries in Europe is from 1921 as a PhD thesis!
However, Cahill is a bloody good writer. Lively and witty and I went along with most of what he wrote: Pleasurable meanderings through Augustine's writings (both irreverent and serious), Saint Patrick, Irish mythology and poetry (not especially germain and a bit of a bore really), Classical Roman literature, Irish missionaries.
If only all history could be written like this - even if it's a bit wonky on the old Irish bias.