Leiber has stretched out a very flimsy story line into a 50-page trivia-fest on the number seven. A genius of a mathematician yearns for his childhood ability to visualize and play with mathematics as if it were a real, physical space in which he could move mentally at will - sadly, that ability withered away as he matured. He ends up beseeching the "Great Mathematician" to return him to that mathematical realm or end his life. [Ironically, it is the mathmatician's firm belief that Mathematics is just a game and numbers have no independent existence outside of human mind, despite his longing for the mathematical space...]

Almost immediately after his invocation, an alluring woman, ostensibly from the Pythagorean space where numbers are real, appears at his front door. They end up playing a very, very long word game involving the number seven (which is witty at times and quite tedious at others). Along the way, the mathematician launches several harangues against Pythagorean mysticism, Newton's alchemy, etc. Finally - and after substantial sexual innuendo and explicitendo - the woman and the mathematician vanish when he breaks a strange figurine belonging to the woman; the implication is that they have retired to the Platonic world of forms.

There is a lot of non-mathematical information in the story which a trivia-buff should love and some good/funny/stereotypical lines:

after 35 years i read this novel again. translation in dutch, so i cannot judge the original text. excellent reading, even more so after all this time.

as most sf of that era, the novel is quite dated. a time of dreams, and hope, or so it seems often to me. lost, i'm afraid, as such. but then, by now i am an elderly jaded man, a bit lost myself. about fifty pages of text. all around the number seven. and around the essence of sexual/emotional dreaming of the younger. which does not disappear with the passing of time, just gets hidden more deeply.

i am not a mathematician, nor a literary critic, not even a psychologist. but i know what i see, eat, and read. and this story fills mind and soul, just for a while, as it is intended. the travel around the number seven is exciting. the innocent and honest sexuality is exciting. and, very importantly, these subjects take over just before one of them becomes too heavily charged.

in short, lovely reading, very interesting, and still very erotic.