FORGOTTEN BOOK: THE WATER OF THOUGHT

The Water of Thought by Fred Saberhagen  (first published as one half of an Ace Double, 1965; greatly expanded under the same title in 1981; included in the omnibus The Space Force Chronicles, 2014)

Fred Saberhagen (1930-2007) was a popular and best-selling science fiction author, best known for his Berserker series and novels about killer machines that roamed the universe looking for intelligent life to exterminate.  The Water of Thought, published two years before his first Berserker collection, was Saberhagen's second published book and the third  and final entry in his Space Force series, which began with his second published story, "Planeteer" (Galaxy Science Fiction, April 1961), and continued with his first novel The Golden People (1964, another Ace Double).   The first Berserker story, "Fortress Ship," was published in January 1963 and appears to have influenced a portion of The Water of Thought (and, possibly, also The Golden People, which I have not read).

The protagonist of the Space Force series is Boris Brazil, a planeteer (or planetary explorer) for the all encompassing Space Force.  Much of the galaxy has been settled in one fashion or another and explored (although at times rather incompletely), including the planet Kappa, located in a remote, less traveled section of the galaxy.  Humanity's presence on Kappa appears to be only a small enclave situation far enough away from the natives to have only occasional contact with the primitive Kappans, who are somewhat humanoid in appearance.  The Kappan society is divided among the workers, the warriors, and the priests.

Located somewhere on the planet is the Water of Thought, a strange elixir of almost magical powers.  It is actually water from a pool deep in the territory of the hominids, a race of primitive pre-humans unknown to the few Earthmen on the planet.  The hominid society is far more primitive than that of the Kappans, and the Kappans have been known to take the hominids as slaves to be worked to death and brutalized.  Both the Kappan and hominid societies are far more complex than anyone, even themselves, realize.

From the interior cover blurb:  

"Was that the key to a world forgotten?

"One explorer had already disappeared on the primitive planet, Kappa.  So the day a second Terrestrial, Jones, ran away after drinking the sacred Kappan water that he had coerced the natives into giving him, the remaining planetologists meant to find out just what was going on.

"Questioning the aliens only deepened the mystery.  For they said that what Jones had drunk would enable him to communicate with his animal ancestors.  It was their most precious and sacred possession.

"But how could it effect a person never born on Kappa, a person without such 'animal' ancestors?  what would really happen if either of them managed to bring this incredible liquid back to Earth?

Given the bloviated and often inaccurate plot descriptions common to Ace Doubles, it's obvious that there is more going on here.  The book centers on seven Terrestrials:

• Boris Brazil, the planeteer protagonist and hero of the novel; he landed on Kappa for a brief stopover until a scheduled Space Force ship will be able to take him to Earth for some much needed R-and-R.  When he first tasted the Water of Thought he lost all free will and had to obey every command from...
• Edmund Jones, another planeteer, one who plans to spend his time on Kappa.  When he first tasted the Water of Thought, he had visions that obliterated everything but the desire to have more, whatever the cost.
• Emanuel Magnuson, a local anthropologist who had vanished the year before.  Magnuson had discovered the powers of the Water of Thought, which had increased his mania to become the salvation of Mankind, leading it newer and greater glories, even if that meant thinning  the herd of undesirable humans; Magnuson was also convinced that he could make the hominids "evolve" to full humanity and thus usher in a glorious new age.  To help in his plan, he contacted...
• Don Morton, a local smuggler.  Magnuson managed to get sample of the Water of Thought to Morton, who arranged for them to be shipped to a large criminal cartel.  The profits from selling just a small amount of the elixir were astounding.  Morton was a naturally cruel and avaricious person.  Drinking the water mad his rage, greed, and egomania expand many-fold into a homicidal mania.  To aid in getting the water off-planet, Morton brought in a partner...
• Mayor Pete Kaleta, the leader of the small Terrestrial enclave.  Kaleta is weak and greedy.  The water made his greed an obsession, erasing any bit of common sense he might have had.
• Brenda, one of the few local unattached women in the enclave.  She finds herself attracted to Brazil, and he to her.  The water has made her inhibitions vanish and she offers herself to Brazil, and she risks her own life to aid him.
• Jane, the other "unattached" woman in the enclave, although she is in reality heavily attached to Morton.  Jane has a weak will and knows that she is doing wrong, but has a hard time preventing it.

For a short novel, The Water of Thought packs a lot into it.  Often chaotic in its reading, the book manages to pull most of the threads together in the end.  The most interesting parts include the dissection of the to alien societies, the true planarian-like secret of the Water of Thought, and Brazil's attempt to stop the homicidal Morton, who is wearing an invulnerable and deadly "groundsuit," sort of a precursor to Saberhagen's berserkers.

A fast read with more to it than appears on the surface.