"Rikki-Tikki-Tavi" begins with introduction of the readers to the main character and some of the supporting characters of the story. Rikki-tikki is a mongoose, a ball of energy contained in a body of fur.
The rising action follows Rikki-Tikki as he explores the bungalow and the garden, encountering Nag and Nagina for the first time. He senses that these are enemies but does not fully engage in battle with them at this time.
He was afraid for the minute; but it is impossible for a mongoose to stay frightened for any length of time..."Well,'' said Rikki-tikki, and his tail began to fluff up again, "marks or no marks, do you think it is right for you to eat fledglings out of a nest?''Nag...wanted to get Rikki-tikki off his guard. Rikki-tikki...jumped up in the air as high as he could go, and just under him whizzed by the head of Nagaina, Nag's wicked wife.
Rikki-Tikki does engage in red-eyed mongoose fury with Karait, the brown snake, and becomes the hero of the human family when he successfully kills the snake.
The climax of the story is Rikki-Tikki's killing of Nag. He attacks Nag as the huge snake sleeps, using all the mongoose instinct he possessed to make up for his lack of experience in fighting cobras.
"It must be the head,'' he said at last; "the head above the hood; and when I am once there, I must not let go.'' Then he jumped. The head was lying a little clear of the water-jar, under the curve of it; and, as his teeth met, Rikki braced his back against the bulge of the red earthenware to hold down the head. This gave him just one second's purchase, and he made the most of it.
Having killed Nag, Rikki-Tikki realizes that Nagina will be hunting for him. The falling action covers the development and carrying out of the plan to trick and destroy Nagaina and the baby cobras in her nest. With help from some of the others, Rikki-Tikki succeeds in luring Nagaina away from the people and follows her into the hole that was her den.
Darzee sings a lament to mourn Rikki-Tikki's death, which starts the resolution and continues until Rikki emerges from the cobra's hole and announces that Nagaina is dead. The word of the victory spreads through the garden and among the humans. Rikki-Tikki-Tavi is the hero, and he spends the remainder of his life patrolling the garden "with tooth and jump and spring and bit."