Trama

As a result of the Berlin Conference, the Congo is divided up between Belgium and the United Kingdom. The Belgian government is on the verge of bankruptcy, having gone into heavy debt to build a national railway and other infrastructure. In response, King Leopold II of the Belgians decides to extract the Congo's rich mineral deposits, sending his envoy Léon Rom (Christoph Waltz) to secure the fabled diamonds of Opar. Rom's expedition is ambushed and massacred, with only Rom surviving. A tribal leader, Chief Mbonga (Djimon Hounsou), offers him the diamonds in exchange for an old enemy: Tarzan.

In London, the man once called "Tarzan" has long since left Africa behind and settled down with his wife, American aristocrat Jane Porter (Margot Robbie), and has taken up both his birth name and ancestral family residence as John Clayton III, Lord Greystoke. In the eight years since returning from Africa, Lord Greystoke's story as Tarzan has become legendary among the Victorian public, although Lord Greystoke himself wishes to leave the past behind him.

Through the British Prime Minister (Jim Broadbent), he is invited by King Leopold to visit Boma and report on the development of the Congo by Belgium, though Greystoke politely declines the invitation. An American envoy, George Washington Williams (Samuel L. Jackson), who recognizes John from the stories of "Tarzan", privately reveals to John, Lord Greystoke, that he suspects the Belgians are enslaving the Congolese population and persuades him to accept it in order to prove his suspicions. Jane is disappointed when John tells her that she cannot come, as he believes the trip to be too dangerous, remembering how both his parents died as a result of the jungle's brutality following their shipwreck there - his mother died of disease, and his father was later killed by the Mangani apes, leaving the baby John to be raised as Tarzan by his ape "mother" Kala and "brother" Akut. However, Jane reminds him that she grew up in Africa as well and misses her home. John relents and allows Jane to accompany him.

John, Jane and Williams take their trip to the Congo. There, the trio encounters a tribal village that knew John and Jane during their stay in the jungle. Jane explains to Williams that her husband was once considered an evil spirit by the African tribes, including that of Chief Mbonga. She recalls how, when she was younger, she and her father lived in the tribal village helping to care for local children. There she met Tarzan, who shielded her from a vicious ape attack, saving Jane's life but was severely injured in the process. Jane took the injured Tarzan home, nursed him back to health, and the two fell in love. That night, as the tribe sleeps, Rom and his mercenaries attack the village and kidnap John and Jane and kill the tribe's leader. They then escape to a nearby steamboat with Jane and several of the tribe's members as slaves, but Williams is able to rescue John.

With the aid of the tribe's warriors, John and Williams pursue the steamboat and en-route, intercept a Belgian military train carrying captured slaves, providing Williams with the evidence he needs to expose King Leopold. They capture an engineer on the train who reveals that Leopold is building a massive rail infrastructure, that once completed, will put 60% of Congo within 3 days of a fort. But the promised army of 20,000 has not yet arrived to take possession of the forts. They also discover that Rom intends to use the diamonds to pay for a massive army to subdue the Congo and allow Belgium to mine its wealth for Leopold's benefit.

As John and Williams continue onward, John encounters the adult Akut from his old tribe, who is now leader of the apes. Aware that Akut considers him a deserter, John challenges him to a fight and loses. That night, as John recovers, Williams recalls the massacres of Native Americans during the Civil War, comparing his actions to be as bad as Rom's and Leopold's.

On Rom's steamboat, Jane dines with Rom, before escaping and swimming to shore. Jane stumbles into an ape nest, where she is rescued by Rom, whose men then shoot and murder many of the apes. John saves the remaining apes, reconciling with Akut, before pursuing Rom. He is cornered by Mbonga and his tribe, where it is revealed that John once killed Mbonga's only son for previously murdering Kala. A defeated Mbonga tearfully accuses John of lacking honor, as his son was just a young boy when John killed him. John spares Mbonga, just as Akut and the apes arrive to subdue the tribe.

Rom takes Jane and the diamonds to Boma, where he plans to take control of the mercenary army who has finally arrived by sea. John, Williams and Akut trigger a massive stampede of wildebeest through Boma, destroying the town and distracting the soldiers, allowing John to rescue Jane. As Rom attempts to escape by boat, Williams sinks it with a machine gun as John swims aboard. Rom tries to kill John, before John throws Rom into the water, where he is devoured by crocodiles.

Williams returns to England and presents the Prime Minister with evidence exposing the slave trade in the African Congo. One year later, John and Jane, having remained in Africa and settled in Jane's father's old house, welcome their first child, as John, Lord Greystoke, returns to his rightful place among the great apes as Tarzan.