A firm advocate of the reality of Atlantis. In the seven books he wrote on the subject, including The Problem of Atlantis (1924), he drew on evidence from geology, biology, and archaeology to substantiate the ancient myth. He drew a parallel between the decadence of the ancient Atlanteans and the present- day Europeans, particularly the German Nazis, and predicted a similar fate for Europe unless its inhabitants mended their ways and returned to the true faith. He developed his argument in Will Europe Follow Atlantis? (1942). He was particularly incensed by the Nazi claim that Atlantis was the original home of the Nordic race, the Atlanteans in his opinion having been Anglo-Saxons, and focused his attack on the Germans and their Satanic practices in The Occult Causes of the Present War (1944).
Spence wrote more than 40 books, including The Magic and Mysteries of Mexico; The Problem of Lemuria (1932), An Encyclopedia of Occultism (1920), and The Occult Sciences of Atlantis (1943). He was vice-president of the Scottish Anthropological and Folklore Society, and in 1951 he was awarded a Royal Pension for Services to Literature.