In Macbeth, who tells Fleance to escape?
Macbeth has ordered the murders of Banquo, his former best friend, and Banquo's son, Fleance, as a result of his fears that Banquo will father a line of kings. When the Weird Sisters presented their prophecies to Macbeth -- that he would become Thane of Cawdor and King of Scotland -- they also told Banquo that, though he would never be king himself, he would "get kings." Now, Macbeth is embittered by the idea that he has murdered Duncan so that he could be king a short time and then pass the throne on to Banquo's issue rather than his own.
Macbeth sends three men to murder Banquo, so he can have no more children, and Fleance, so that he can never rule or produce children of his own. They succeed in surprising the father and son, and they mortally wound Banquo. However, Banquo has time to order his son to flee the scene, and Fleance does escape. In fact, as Shakespeare was well aware, the king at the time Macbeth was first performed was James VI of Scotland (James I of England), and this king could actually trace his lineage back to the historical Banquo. Thus, the Weird Sisters were right!
In Act III, scene iii, of Macbeth, three murderers attack Fleance and Banquo outside of the Macbeth's castle at Inverness. Banquo screams, "Fly, good Fleance, fly, fly, fly!" (III.iii), telling his son to escape.
Banquo: O, treachery! Fly, good Fleance, fly, fly, fly!
Thou mayst revenge. O slave!
[Dies. FLEANCE escapes] (III.iii)