Sakhmet's bond with Ra was so great that her powers allowed her to force a red sun shine from the Umbra even in the night. The Week of the Midnight Sun was intended to end the dominion of Set and his childer. Sakhmet slaughtered the herds of the Setites, spread vile diseases, and fought several of his childer, among them the Scorpion King. Sakhmet's fate is not recorded. Some believe that she burned herself up with Ra's power, others that she regained her senses.
The Week of the Midnight Sun drove the Setites into hiding, allowing the followers of Horus to conquer Upper Egypt and unite the Two Lands. As a result, Set and his followers took a special interest in the Bastet (and by extension, the Garou) from that night forward.
For mythological goddess that inspired the character of Sakhmet, see Sekhmet.