The book's heart is the Mowgli cycle, which opens when a human toddler wanders into a wolf cave in the Seeonee hills, just ahead of the lame tiger Shere Khan, who claims the child as his kill. Mother and Father Wolf shelter the boy, and Mother Wolf names him Mowgli the Frog and vows he will live to hunt the tiger who hunts him.
To stay, Mowgli must be accepted by the Pack at the Council Rock under the Law of the Jungle. Baloo the bear, who teaches the cubs the Law, speaks for him, and Bagheera the black panther adds the price of a freshly killed bull. So Mowgli is entered into the Pack for a bull and on Baloo's word, and grows up learning the speech and ways of every jungle people.
The peace cannot last. As the old leader Akela weakens, Shere Khan turns the younger wolves against both the aging chief and the man-cub. Warned by Bagheera, Mowgli fetches fire, the Red Flower that all beasts dread, and at the decisive Council he scatters the wolves, shames Shere Khan, and saves Akela. Then a wholly new feeling overtakes him: he weeps, and Bagheera tells him these are the tears of a man, the sign that the jungle is now closed to him.
Around this central arc the book gathers other tales. In Kaa's Hunting, the lawless Monkey-People, the Bandar-log, snatch Mowgli, and Baloo and Bagheera enlist the great python Kaa to rescue him, setting the rule-bound Jungle-People against a tribe with no law, no leader, and no memory. Other stories step away from the jungle entirely: a young white seal hunts the seas for a beach where men cannot club his people; a fearless mongoose named Rikki-tikki-tavi fights the cobras Nag and Nagaina to protect an English family; and a boy, Little Toomai, witnesses the secret nighttime dance of the wild elephants.
Verse threads the whole collection, since each story is framed by a song in the voice of its creatures, from the Night-Song in the Jungle to the chants of the seals and the camp animals. Taken together the tales make the natural world a society with its own customs, ranks, and tests, and they keep returning to one question: what a creature owes its own kind, and what happens when it cannot fully belong to any.