What is the complication that's follows the killing of nag in Rikki-tikki-tavi?

After Rikki-Tikki-Tavi kills Nag, the male cobra, a significant complication arises when Nagaina, Nag's mate, seeks revenge. She threatens the safety of Rikki's human family by trying to access their home and plans to kill them to avenge Nag's death. This conflict heightens the tension in the story as Rikki must confront Nagaina to protect his adopted family, ultimately leading to a climactic battle for survival.