The ghost of Banquo appears in the fourth scene of Act III as Macbeth and Lady Macbeth are entertaining their guests at dinner. Before the banquet, Macbeth had engaged the services of two murderers to waylay Banquo and Fleance and kill them; during the banquet, one of the murderers appears with news that Banquo is dead but Fleance has escaped. This news unnerves Macbeth, but at his wife's direction, he tries to hide his discomfort and play the part of host. Quite cynically and ironically, he welcomes his guests by wishing that Banquo were among them.
It is a short time later that Banquo's ghost, covered in blood, appears, but only Macbeth can see him. The sight unhinges Macbeth completely. He is terrorized. He speaks directly to Banquo's ghost:
Thou canst not say I [killed you]. Never shake
Thy gory locks at me.
Lady Macbeth tries to control her husband's strange behavior and to explain it to their guests, but Macbeth's fear, and what appears to be insane babbling, cannot be contained as he continues to react to Banquo's ghost. Finally, Lady Macbeth dismisses the guests, asking them to leave immediately.