The Mind Parasites by Colin Wilson (1967): English writer Colin Wilson started off critical of H.P. Lovecraft. But after being challenged by Arkham House founder August Derleth to try to write a Lovecraftian piece of fiction, Wilson ended up writing at least three Lovecraft-tinged novels and one novella.
However, what makes The Mind Parasites one bonkers addition to the Mighty Lovecraft Tradition is Wilson's own life philosophy, sometimes described as 'optimistic existentialism' or 'phenomenological existentialism.' Basically, human beings need to be positive. And we can map subjective experiences of the mind as if they were objective and quantifiable phenomena. And...
Well, Wilson pushes these concepts in The Mind Parasites into the realm of super-powers that the right person can attain, basically, by thinking real hard for a few days.
This leads to a lot of philosophical discussion, much of it bat-shit crazy, and all of it in service to a plot in which ancient 'Mind Parasites' have been keeping humanity from reaching its super-powered potential for at least 200 years.
Lovecraft gets name-checked along the way, his stories re-imagined as dream visions of the way the universe operates. Whatever horror there is occurs early in the novel, before people start developing earth-shaking super-powers. It's the early stretches that are most Lovecraftian, as details accumulate and parallels with Lovecraft's "The Call of Cthulhu" are most prominent.
The main events of the novel take place in 1997, 30 years after The Mind Parasites was written. Wilson gets a lot wrong about the then-future. Indeed, it isn't clear until the climax why the novel had to be set in the future. Then we find out. Oh, brother, do we find out!
The basic set-up of the novel -- in which a few plucky, intelligent men In the Know must band together against a massive menace -- recalls some of Lovecraft's works, as well as a lot of other science fiction (Robert Heinlein's Sixth Column, a.k.a. The Day After Tomorrow, much resembles this work, though there the menace is human and the super-powers used to combat it derived from new engineering and scientific discoveries). One also sees the echoes of Eric Frank Russell's Sinister Barrier, in which humanity faces hitherto unseen alien enemies. It's very much a science-fiction trope, and Wilson's heroic cadre of super-thinkers become that old stand-by, The Secret Elite, in order to save humanity.
Wilson's exposition can be heavy-going at times. And while ostensibly inspired by Lovecraft, the novel very quickly moves into the more optimistic Derleth Branch of Lovecraft-inspired fiction: these evils can not only be combated, but utterly annihilated. Brian Lumley's 1970's HPL-homages in his Titus Crow novels would go down this same path, turning Lovecraft's grim cosmos into a backdrop for zippy, pulp-fiction heroics. And while there's a lot more philosophical talk in The Mind Parasites than in Lumley's early work, the last fifty pages or so head straight to Pulp-land, Destination: E.E. "Doc" Smith. Surpassingly odd but lightly recommended.