The item that does not belong in the group is Fleance, as he is not involved in the murder plot that characterizes the actions of the other three.
Macbeth, Banquo, and the murderer are all directly tied to the themes of ambition and treachery in Shakespeare's "Macbeth." Macbeth, driven by his desire for power, orchestrates the murder of King Duncan and seeks to eliminate Banquo, who poses a threat to his crown. Banquo himself is aware of the prophecy regarding his descendants and is ultimately murdered by Macbeth's hired assassins to prevent the prophecy from coming true. In contrast, Fleance, Banquo's son, represents the potential future of the royal line but remains innocent and untainted by the murderous ambitions that define the other characters' actions. Thus, while Macbeth, Banquo, and the murderer navigate the dark consequences of ambition, Fleance remains a symbol of hope for a future unmarked by treachery.