David Gurney - The Conjurers

Originally published in the U.S. as "The Demonists" in 1971. This re-titled U.K. edition published by New English Library (ISBN: 0450022366) is dated September 1973. Davis Gurney was a pseudonym of Patrick Bair. Not sure what the NEL art dept. were thinking with this cover, it doesn't exactly cry out 'horror and the supernatural.'