At the beginning of the story, Rikki finds himself washed away from his home to the bungalow where Teddy and his parents live. During this scene, which is set near and inside the bungalow, the mood is innocent and happy. Teddy and Rikki are both youngsters, and they enjoy playing and finding out about the world without the threat of harm. Rikki runs around the table, climbs on Teddy's shoulder, and explores the house at night. The conflict to come is foreshadowed when the father mentions a snake coming through the nursery window and the mother can't entertain such a thought.
In the morning, Rikki goes out to the garden, and the mood changes. Darzee is crying pitifully, and he introduces an intense and dangerous mood as he reveals that the cobra has eaten a baby bird. Soon the menacing cobra appears, and the mood intensifies as Nag and Nagaina almost succeed in killing Rikki. Quickly the life-and-death nature of life in the garden becomes clear. Rikki's battle with Kurait, who could have killed Teddy, continues the suspense.
Back in the bungalow that evening, the mood becomes somewhat comical as Rikki talks to Chuchundra, the cowardly muskrat. As Rikki overhears the wicked plotting of Nag and Nagaina and as Nag slinks into the bungalow, tensions heighten again. The fight with Nag is dangerous and scary.
The next day in the garden, there is a triumphant mood created by Darzee's song of praise, but Rikki quickly creates intensity again as he plots to distract Nagaina while he destroys her eggs. The scene on the veranda as Nagaina has Teddy in a dangerous position becomes increasingly suspenseful until Nagaina "flew like an arrow down the garden path, with Rikki-Tikki behind her." While Rikki is underground fighting Nagaina, with only Darzee's death song as a play-by-play, the mood becomes somber and foreboding.
When Rikki reappears and trots over to lie in the grass, the mood shifts to one of joy and contentment because of Rikki's victory over the snakes.