In between ministering to the needs of his parishioners, Canon Doble pursued a lifelong study of sub-Roman Celtic Britain and Brittany, in which he gained a European-wide reputation. He was especially interested in the medieval vitae or 'lives', and additional legends, related to the early Christian holy men and women (or 'saints') of Cornwall, Wales and of Brittany. The fruit of his research was published between 1923 and 1945 in a collection of forty-eight booklets known as the "Cornish Saints Series". The later issues (from 1928) include historical commentaries by Charles Henderson. They have since been republished in book-form but without the Henderson commentaries: this edition was edited by Donald Attwater and appeared in 5 volumes published by the Dean and Chapter of Truro, 1960–1970. Until Orme's "Saints of Cornwall" was published in 2000, they were the most thorough, scholarly and reliable works available on the subject.