Kim is a half-caste orphan son of a British soldier and a nursemaid who runs free on the streets of Lahore and who incidentally makes contact with the British secret service. He attaches himself to a Tibetan Lama who is on a quest to be freed from the Wheel of Life. He becomes his chela, or disciple, but is also used by the British to carry a message to the British army in the North. Kim's trip with the Lama along the Great Trunk Road is the first great adventure in the novel.
Kim is recognized by chaplain of his father's army regiment and sent to school, but keeps in touch with the Lama and also with his secret service connections. He is trained in espionage; the game of looking at a tray full of mixed objects and noting which have been added or taken away is still used for training spies and is still called "Kim's Game".
Kim rejoins the lama and takes another trip north, this time capturing papers from Russian spies but at the same time the Lama continues his spiritual quest. At the end of the novel, Kim is undecided between the spiritual life of the Lama and the life of action at which he excels.
In 2001, the book was listed as one of the 100 best English-language novels of the 20th century by the editorial board of the American Modern Library.
Two novels by John Eyton, Kullu and the Carts and Kullu and the Elephant (c. 1929), are clearly derivative of Kim; likewise, Eyton's Jungle-born (1925) appears to borrow elements from the Jungle Books.