A mysterious cosmic phenomenon is detected. An unscrupulous scientist lies to and bullies political leaders until he gets to create a society of super-scientists, ruled by himself and independent of any governmental oversight. By the time his lies about the consequences of the phenomenon (he predicted the end of the world, not entirely accurately) become apparent, he has kidnapped the Prime Minister and managed to arrange things so that he is, basically, Dictator Of The World, and only a few tens of millions of people died in the process.
Now, that sounds as if it could be a good, though extremely bleak, read. However, that's not quite how things work in 'The Black Cloud'. For one thing, Mr Dictator is the hero. For another thing, we are meant to sympathise with his view that the people and their elected representatives should have no place in government because, well, they're not scientists like him and his mates, are they? A position that the author clearly endorses.
Welcome to the strange world of Fred Hoyle, denier of evolution, the big bang, and most forms of rationality. Just to add to the mess, not only is this book basically a nasty little quasi-fascist tract on the basic superiority of the 'scientist' (and the obvious inferiority of women), but those scientists who are out last best hope are so utterly, utterly full of themselves that they fail to spot the fact that should have been obvious from the outset: if a cosmic 'thing' just happens to be perfectly aimed at the Earth, in spite of having originated outside of the Solar System, it is most likely that it is not simply the workings of chance. In other words, as Arthur C Clarke correctly observed in 'Rendezvous with Rama' - there are aliens at work. Hoyle's super-scientists are, however, better than you, me and Clarke: they know there are no aliens, so they feel quite happy to ignore the observational evidence that contradicts their pet theories for, oh, about 130 pages.
Now add in that the whole thing is stupendously boring. It consists of long, long scenes of scientists indulging in talking scientific shop. At one point, we even get a footnote so we can follow the equations being written on a blackboard! There's no drama, no movement, just endless discussion of what happens when two masses of gas hit one another while moving quite fast, or what ionising radiation is, or why it can't be aliens driving the thingy, despite it slowing down and parking itself by the Sun.
So is it, as the blurb says 'SF at its highest level'? No, it's the badly written fantasy of a nasty little man, who couldn't bear the thought that he didn't get to rule the world, and thought that women were basically stupid and fit only to make coffee and be the objects of sexual harassment.
Flee from it. Flee like a little, frightened child.