A sort of premonitory tremor, a fear of he was not certain what, had passed through Winston as soon as he caught his first glimpse of the cage. (which is quoted from the sixth or maybe the ninth paragraph in the fifth chapter in the third part of the novel.)
When I was reading Orwell's 1984, I found the phrase "a fear of he was not certain what" difficult to understand. What is the meaning of it? I would appreciate it if you would answer my question.
I would also like to know how the phrase is constructed grammatically, if you could tell me.