The Magician. by W. Somerset Maugham

In Paris, surgeon Arthur Burdon and his fiancé are introduced to Oliver Haddo, a wealthy Englishman from an old family who claims to be a magician trained in the occult. At first they are unconvinced and irritated by Haddo's boasts ; however he soon demonstrates his powers in more and more fateful ways. The character of Oliver Haddo is an unflattering caricature of the English occultist Alistair Crowley, whom Maugham had met while living in Paris.
Crowley himself wrote a review in Vanity Fair in which he accused Maugham of plagiarizing various other novels, signing off as "Oliver Haddo". Most critics dismissed these allegations.