The two murderers lie in wait a mile from the royal castle. A third murderer joins them, sent by Macbeth.
The Third Murderer is an unsolved mystery. No critics know who he is or why he's there.
Banquo and Fleance enter. The murderers attack. Banquo is killed, but Fleance escapes. The murderers return to the castle to tell Macbeth what's happened.
Macbeth's effort to control fate seals his doom. Fleance lives and Banquo's death makes the Thanes suspicious.