When Rikki-Tikki destroys all of the eggs except one, we know that he will need to face off against Nagaina and kill her in order to survive.
Foreshadowing is a hint earlier in the story about what will happen later. At the climax of “Rikki-Tikki-Tavi,” Rikki-Tikki has killed Nag and destroyed most of Nagaina’ eggs. He realizes that “cobra's eggs meant young cobras later on.”
Nag and Nagaina are also threatened by Rikki-Tikki.
"When there were no people in the bungalow, did we have any mongoose in the garden? So long as the bungalow is empty, we are king and queen of the garden; and remember that as soon as our eggs in the melon-bed hatch (as they may to-morrow), our children will need room and quiet.''
The main conflict in the story is between Rikki-Tikki and the snakes. The snakes are a threat to the humans. As Chuchundra says, ``Those who kill snakes get killed by snakes.”
Rikki kills Karait, Nag, and all but one egg. Then he needs to kill Nagaina and crush the one last egg in order for everyone to be safe.