This was Iain Banks' 2nd published novel (1985), after 'The Wasp Factory.'
It's really 3 separate stories, which are only-sort-of interconnected. That is, there are some references, recurring motifs, etc, but I didn't think they reflected on one another as much as they could have. Even Banks has, said, reportedly, the book "didn’t do exactly what it set out to do and I think you have failed to an extent if the reader can’t understand what you’re saying."
I don't think it was incomprehensible, I just think that at this point Banks was not quite as adept at playing with structure as he has since become. Still, I have not yet read a Banks book that I didn't really really like, and this is not an exception.
The stories are:
In 1980s, UK, art student Graham is introduced to the enigmatic Sara ffitch by his eccentric best friend, Slater. He instantly falls for her, hard, and moons after her with such a mad crush that the reader can just tell that it's probably unrequited and not all will turn out well.... especially since Sara's rumored to be seeing a tough biker dude...
In the same time and place, a paranoid schizophrenic, Steven Grout, is having a hard time with his life. His odd way of looking at things and lack of self control have just lost him his job - again. He believes he's really a warrior in some Interplanetary conflict, and is searching for the Way Out in sci-fi novels - but it's hard when he constantly has to try to avoid Microwave Guns and more mundane trials.
In another place altogether, a surreal castle outside of time, two actual warriors are being punished for their conduct in the 'Therapeutic Wars.' In a decaying castle made of books and lit by bioluminescent fish, trapped in elderly bodies, the former enemies are forced to play bizarre, random games and to try to answer a nonsensical riddle.