Tarzan (Johnny Weissmuller), Jane (Maureen O'Sullivan), and Boy (Johnny Sheffield) are enjoying a swim their jungle paradise when then see an airplane landing on their isolated escarpment. It has brought a group of trappers who plan to capture wild animals for their travelling circus back in the States. Buck Rand (Charles Bickford) the lion hunter aims his rifle at Tarzan who breaks the gun and orders them to leave the next morning. They take advantage of the time to trap lions and other animals. Boy, fascinated by the visitors and their aircraft, shows up at the plane with his elephants and impresses the hunters with his rapport with animals. Realizing that this wild boy of the jungle could make them a fortune back in America, Buck offers Boy a ride, but pilot Jimmie Shields (Paul Kelly) warns the boy to leave. Boy returns to distract a lion to save Manchester Montford (Chill Wills) who has become caught in a net. Buck shoots the lion, hostile natives attack, Boy calls Tarzan but Tarzan and Jane accidentally fall while swinging in on vines. While Tarzan and Jane lie unconscious, the natives start a fire,  Buck and the party escape with Boy on the plane. Cheetah rescues Tarzan and Jane from the fire by dropping them a vine. Boy's parents and Cheetah immediately start overland to the coast where they use gold to buy civilized clothes from a Chinese tailor and to book passage on a flying boat mail flight to New York to rescue their son.

Upon reaching New York they take a taxi to a hotel. There are many comedy scenes as Tarzan and Cheetah try to adjust to all the complexities of civilization. Tarzan hears what he believes are native war dances and a woman screaming for a witch doctor on the musical programs on the cab driver's radio. Tarzan showers in his suit, Cheetah eats makeup, and cause major disruption in the classy hotel. Jane and Tarzan go to a club to find Jimmie and meet the club's singer, Jimmie's girlfriend, Connie Beach (Virginia Grey), who fills them in on Buck's circus. Meanwhile,  Col. Sergeant (Cy Kendall) and Buck get a $100,000 offer for Boy from Brazil.  Tarzan and Jane arrive at the circus and a custody battle for their son begins. Tarzan is out of step with the conventions and laws of modern man and when things don't go well in court he escapes through a window to climb skyscrapers and  swing through the "stone jungle" in search of Boy. Trying to get to the circus on Long Island he takes a taxi that is stopped by the police on Brooklyn Bridge from which he makes a 250 foot dive into the river. At the circus Manchester is shot while trying to stop Buck and Sergeant. Boy climbs up to the big top trapezebut Tarzan is caught in a net trying to reach him. He is locked in an animal cage. The elephants come to the rescue -- again -- they free Tarzan and trap Buck and Sergeant who are trying to take Boy away  in a car. Tarzan rescues Boy and the villains' car crashes. Back in court, Judge Abbotson (Russell Hicks) sides with Tarzan and even plans to visit them in Africa on a fishing trip. The final scene shows Tarzan, Jane, and Boy cavorting in the water back at their jungle home while Cheetah directs the elephants through tricks with the judge's courtroom mallet.