After receiving the favorable prediction from the Three Witches that he is destined to become the future King of Scotland, Macbeth informs his cruel wife of the prophecy, and she begins plotting King Duncan's murder. Initially, Macbeth is reluctant to follow through with his wife's bloody scheme, but he finally succumbs to his ambition. At the end of act 2, scene 1, Macbeth hallucinates and sees the vision of a bloody dagger leading him to Duncan's chamber as he prepares to kill the king.
Macbeth murders King Duncan offstage in act 2, scene 2. According to Lady Macbeth's plan, she drugs Duncan's servants and leaves their daggers out for her husband. Macbeth then uses the daggers to murder King Duncan in his sleep and before he also kills the unconscious servants. The original plan was for Macbeth to leave the daggers behind in the king's chamber and smear the blood on the servants, which would make it seem like they killed the king. However, Macbeth is too shocked and guilty to carry out the remainder of the plan.
Lady Macbeth scolds her husband for acting like a scared coward and removing the daggers from the chamber. After Macbeth assassinates the king, he is too disturbed to reenter King Duncan's chamber, and his wife is forced to place the bloody daggers back in their proper place. Lady Macbeth tells her husband that he is "Infirm of purpose!" and says, "My hands are of your color, but I shame / To wear a heart so white." Lady Macbeth then brings the daggers back into the king's chamber and coaches Macbeth to act surprised about the crime.