Was he the agent of others or had he some sinister design of his own?
Consider the long sequence of incidents which have all pointed to some sinister influence which is at work around us.
Rolling pasture lands curved upward on either side of us, and old gabled houses peeped out from amid the thick green foliage, but behind the peaceful and sunlit country-side there rose ever, dark against the evening sky, the long, gloomy curve of the moor, broken by the jagged and sinister hills.
He was a son of that Rodger Baskerville, the younger brother of Sir Charles, who fled with a sinister reputation to South America, where he was said to have died unmarried.
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.