Check with a large public library for a copy. Boggles are evil spirits, goblins or bugbears. Bogyman is still in standard usage. The root word is Middle english bugge meaning spirit. Efreet is alternative spelling of afreet, a Moslem supernatural being typically unfriendly toward humans.
Wraiths are ghosts or sometimes spirits that appear to warn of evils to come.
This next is conjecture as Iam not familiar with, nor could I find anything on orknies. The word orc denoted a sea monster which does not seem appropriate in context. But it might be worth looking for a possible connection to the Orkneys. The Vikings who settled in that area were responsible for the complete destruction of Columba's monastery at Iona and sacking Lindisfarne, which was a major center of culture. As a people they were the scourge and terror of the Christian church in Europe.