"The castle of Macduff I will surprise" (4.1.166).
"Whither should I fly?I have done no harm" (4.2.72-73).
"Your castle is surprised" (4.3.204).
4.1: Macbeth visits the witches to ask them about his future. The witches allow Macbeth to see four horrible visions. The first three are visions that Macbeth understands, but he is confused by the final vision. Lennox then enters and tells Macbeth that Macduff went to England, and Macbeth sends murderers to kill Macduff's family.
4.2: Lady Macduff tells Ross that she feels betrayed by her husband since he left. Ross tells her to trust him, and he then leaves. Someone later warns her that she is in danger, but she refuses to leave. Murderers then enter the castle to kill her and her son.
4.3: Macduff meets Malcolm in England, and Malcolm tests Macduff's loyalty by talking about whether or not he should be king, and Malcolm decides that he can trust Macduff. Ross later arrives and tells Macduff that his family is doing okay, and the three of them then make a plan to return to Scotland. Ross then says that he lied about Macduff's family and he tells him that Macbeth killed them.