The Space Vampires by Colin Wilson (1976): Wilson mentions Canadian Golden-Age science-fiction great A.E. Van Vogt in this novel's acknowledgements section. That reference clarifies a lot of the zaniness of this novel's construction, not to mention its philosophizing.
Even in his first short story, "Black Destroyer" (1939), one of two Van Vogt stories that allowed him to get a settlement from the makers of Alien (1979), the Winnipeg revelator combined horror, science fiction, and some exposition-heavy stretches of philosophizing about human society and social engineering. And a lot of Van Vogt's protagonists ended up as supermen in the end.
The Space Vampires starts off, much like the later Alien, with the discovery of a derelict alien ship by an Earth ship. We're at the end of the 21st century, and humanity continues to explore the solar system. These first fifty pages or so give us an effective shot of cosmic horror and wonder. The derelict is cyclopean in size and mysterious inside. Humanoid aliens rest in what seem to be tombs. But if the crew was human, why does the interior scale of the ship, like the exterior, suggest a dark cathedral made for giants?
And what's up with the frozen, alien octopi?
So far, so good. The horror elements remain effective when the explorers return to Earth with three of the preserved alien bodies. A horrific event occurs in London, England, which for some reason seems to be the headquarters of Earth's space command (shades of the Quatermass series and Doctor Who!).
And then Colin Wilson does the writerly equivalent of crapping his pants over and over again in an explosive diarrhea spout of increasingly ridiculous theories spouted by talking heads that only occasionally pause so that the plot can lurch along for a few pages in its inevitable path to a Deus ex machina.
What's impressive about Wilson is that his writing keeps one reading throughout the later stretches of the novel, even as one's suspension of disbelief fades and the tedious stretches of his philosophizing go on and on and on.
To condense everything into a few lines, everything that lives has a life-force. Male and female life forces are like the negative and positive leads on a battery.
The ultimate sexual characteristic of a woman is to submit to the male, which allows for a balancing of the male and female sexual forces. Somewhat counter-intuitively, Wilson's system means that men suck power from women at the moment of orgasm. Among other things, that last bit explains why old men with young wives are virile powerhouses who age more slowly than puny, ordinary men who are stuck with wives their own age (or, I guess, gay men).
There's a whole lot more where that came from, all of it increasingly dire and laughable as the novel shudders to its close. The eponymous aliens can suck the life-force out of anyone, though the learned man can turn the tables on them. So of course our protagonist rapidly goes from alien food source to sex-powered Superman.
Then he learns more about space vampires from an anomalously virile and sexy nonagenerian with three sexy young women living with him. He also realizes that all women are simply expressions of the Eternal Feminine, and that they're there to give him power because he's a man, and men receive power from women either telepathically or sexually because That's the Way It Is! Ha ha whee.
Even though the protagonist is married, he bangs one of the sexy young women because the space vampire is messing with his mind from a great distance because Telepathy! He also mind-melds with another guy's wife to such a level of intimacy while they're just holding hands that she contemplates leaving her husband. Also, she offers some of her life-force energy to him because That's What Women Do! They enjoy having their life energy drained by, um, a man's ejaculating penis. Or just a manly man reading their minds. That's enough. Oh, baby, take my lifeforce!
If nothing else, one can see why film-makers re-titled the movie adaptation Lifeforce. And the movie, wacky and bad as it was, is far superior to the book. By the last fifty pages of the novel, I was hoping the space vampires would kill the protagonist and that annoying nonagenerian (or maybe he was just a late octogenerian. Really, who cares?). Because they are so sexy and virile and hyper-competent. And they'll tell you all about it.
Not recommended unless you stop reading at the 50-page mark and then go off and write your own, better conclusion to the novel. Or if you enjoy masturbating to weird metaphysical/biological fantasies of male sexual power as being an expression of the Infinite.