Sentence:  He could in nowise comprehend it; but, taking it with other previous circumstances, he could not get quit of a conviction that he was haunted by some <WSD>evil genius</WSD> in the shape of his brother […]. 
Meaning of the word marked with <WSD> tags:  The spirit each person is believed to have in attendance, according to certain religious or mythological traditions, which tries to negatively influence him, and is opposed by his (good genius); loosely, someone who is a bad influence.