They Used Dark Forces: Dennis Wheatley

Gregory Sallust Adventure No. VII. It is 1943, World War II, and secret agent Gregory Sallust is parachuted into Nazi Germany. Together with ex-Bolshevik General Stefan Kuporovitch, they join forces with the widow of a German diplomat who is in contact with Allied Intelligence. It is through her that Gregory becomes unwillingly involved with a Black Magician and when, 16 months later, they meet again, each decides to use occult forces in an attempt to destroy Hitler once and for all...