The novel is about cargo cult, a primitive civilizations conducting various acts in order to return with goods from an advanced civilization, like someone entering a blackhole and returning with a 4k tv in 1900s
Astronauts are sent to a space to this place to gain unknown knowledge/ technology, but the astronauts returning Earth are either dead or die in 24 hours. The astronauts won't speak of their experience or are too frightened of their experience
The protagonist is some sort of a social worker/psychologist/ therapist, his duty is to relieve the emotions of those astronauts returning Earth and try to get them to speak up about their experience.
Toward the end, the book mentions some astronauts returning to Earth with a cure for cancer. One astronaut dies in the space shuttle scrawling words around the wall of the shuttle.
The novel is related to lovecraftian horror/ cosmic horror.