The black tower stands half-built in the cheaply bought crash desert land. Workers labor on it with quiet zeal unmappable to any known religion and unrestricted to any arbitrary subset of the human race.

This is only hypothetically correct. Those building the black tower have all been soldiers; legally they remain so, with certain implication vis a vis the distribution of physiological traits. But it's the belief of military laboratories that the effect of PKD82 is broadly independent of biological characteristics.

("PKD82" is the name used by the EU Biological Optimization research group. Laboratories in China and India, and the three different arms of the US military that developed it in mutual secrecy use other names.)

Researchers involved confess to nobody but their coffee cups they would find the phenomenon more palatable if it were less consistent: Humans injected with PKD82 show unmistakable but unparseable changes to their neural function with absolutely no observable change to behavior or capabilities. Approximately three weeks later around 23% of subjects, with no discernable pattern to who, seek a temporary relief from their duties, find others like themselves, and go to the desert to work on the tower for no reason they can explain.

You would think that militaries would be comfortable detaining, torturing, and vivisecting some of them to obtain an explanation. You would be factually correct.

Under torture the subjects do not withhold an explanation for the tower: they don't have one.

PKD82 is the result of new biochemical simulation models applied to the optimization of a pre-existing but failed potential intelligence enhancing drug. Earlier effects on primates showed disturbing signs of success. The only sign from human subjects is the tower. Its design isn't superhumanly sophisticated. Those building it work within their previously measured performance envelopes and die of exhaustion and heat following the usual well-known equations.

Dosing a target population with the drug would presumably disable after three weeks about a quarter of them: the cost-effectiveness ratio is too absurd even for military weapon designers. The project is closed in semi-coincidental simultaneity across all involved military organizations.

The non-responding 77% of subjects is left to the monitoring of a surveillance supplier contractor that gets hit by a silent private equity blitz two weeks later. Monitoring becomes acutely nominal.

Without the constant drip of new people, work on the black tower stops when the last one dies. Conspiracy theories attain their sigmoid curve plateau a few months later, neither too close nor too far from what is known of the truth.

The non-responders intellectual capabilities, were they still being measured, remain the same. They move up, out, and laterally through their organizations at the same rate as their peers. However, they find themselves working in the same teams more often than a null model would predict.

Responding subjects in various forms of captivity continue being studied by teams with diminished budgets and career prospects. As research methods devolve into interrogation techniques they break and confess heinous unnatural crimes and posthuman capabilities that scientists find exciting until matched with the large corpus of interrogation transcripts from the day-to-day operations of every branch of the security industry.

The non-responders work very well with each other without any meaningful hypothesis as to why (none of them has heard of PKD82 by any name, nor are aware of their participation in any experiment). Their teams become comparatively successful, grow, encounter each other, merge. There is an alignment of objectives among them that makes them especially effective, although they cannot express those shared goals and aren't aware of anything to express.