At those moments his secret loathing of Big Brother changed into adoration, and Big Brother seemed to tower up, an invincible, fearless protector, standing like a rock against the hordes of Asia, and Goldstein, in spite of his isolation, his helplessness, and the doubt that hung about his very existence, seemed like some sinister enchanter, capable by the mere power of his voice of wrecking the structure of civilization.
There are no more uses of "sinister" in the book.
Show samples from other sources
They created a sinister plan to recruit terrorists.
In the movie, there was a sinister plot to kill people and harvest their organs.