The hired murderers meet as arranged. On hearing approaching horses, a signal is given, and Banquo and his son Fleance are attacked. The murderers' lantern is accidentally extinguished, and the job is left half-done: Although Banquo is killed, Fleance escapes.
Appropriately, this scene takes place in the dark; the murderers carry lanterns and fail in their duty only when the light is accidentally knocked out and the entire stage is plunged in blackness. But this moment is also highly symbolic, foreshadowed at the end of Act II, when Ross remarks to the old man "By the clock 'tis day; / And yet dark night strangles the travelling lamp." In Macbeth, the forces of darkness seem constantly at odds with those of light.
In contrast to the dark, grisly nature of their job, the murderers' poetic speech is also comparatively light, particularly in the depiction of a traveler reaching the inn at sunset: "The west yet glimmers with some streaks of day; / Now spurs the lated traveller apace / To gain the timely inn" (5-7). One function of such poetry is to contrast the nature of word and deed. We have seen the same hypocrisy in Macbeth himself; he, too, is capable of poetry as well as murder.
Another function is to remind the audience of the existence of natural order and the possibility of salvation. In an ideal world, a belated traveler may hope to find "timely" accommodation, however late the hour. But in a world where the natural order of things has been inverted and in which light is extinguished, as it is symbolically in this scene, that hope is also extinguished. Banquo is riding not toward hospitable welcome but toward his own extinction.
The escape of Fleance is the turning point or peripeteia in Macbeth's tragedy. Banquo's dying words, ordering Fleance to "revenge," remind the audience of the Witches' prophecy to Banquo: that he will be father to a line of kings, even though he himself will not attain the throne.
direction just (4) exact instructions
expectation (10) invitation