I am a total fan of Brian Lumley's Necroscope series. This one, book 4 in the whole series of 13, is especially good. But readers and enthusiasts are possibly ignorant that one of its most central ideas and even some event background, are based on a wonderful shivery long story/ novella by H.P. Lovecraft 'The Case of Charles Dexter Ward', one of the best tales I've ever read. The necromantic activities of Janos, the main Vampire in Necroscope IV, are derived from Lovecraft's story; and even Janos' castle itself and its two original owners are taken from the Lovecraft story! The whole motif of necromancy as such by reducing the cadaver to an essence of salts, and bringing back the rebellious spirit in the thus reconstituted body to reveal secrets by compulsion, and the other motifs of the monstrous shapeless 'guardians' kept in underground tubular holes, comes from 'The Case of Charles Dexter Ward'.
There's absolutely nothing wrong with using Lovecraft's ideas, in fact it is a wonderful tribute & extension of Lovecraft's story; and he would have been the first to delight in it. The original story is so hauntingly good, one longs for more; and for an enthusiast of Lovecraft's novella, like myself, it was an absolute treat to have an author of Lumley's calibre do it justice. Lovecraft himself I believe always encouraged other weird writers to use his mythos, and Necroscope IV shows Lumley's great respect for the story by in fact carefully integrating its events with the references there.
But I think it would have been handsome and appropriate for Mr Lumley to dedicate this chuckaliciously shivery wonderful book Necroscope IV 'To H.P. Lovecraft, author of The Case of Charles Dexter Ward! As an admirer of Lovecraft, he'd surely be the last person to grudge doing so. It would have helped disseminate that wonderful story. I hope he'll do so if Necroscope IV is reprinted.