Here..”He worries that Banquo will be suspicious of Duncan's murder, since he was there when Macbeth received the prophecy that he would be king. He also wants to avoid a “fruitless crown,” so he decides to kill Banquo and his son Fleance in order to ensure that none of Banquo's “issue” take the throne after him.”
Brutus is in his orchard. It is night and he calls impatiently for his servant, Lucius, and sends him to light a candle in his study.