In the early 20th century in Colonial Africa, adventurer Allan Quatermain and anthropologist Jesse Huston are engaged to be married and planning to travel to the U.S. for their wedding. An old friend, Dumont, shows up at their farm and collapses with fever. Dumont is pursued by two tribesmen wearing white hooded masks, but Quatermain chases them off. A delirious Dumont reports he saw streets filled with gold and that Quatermain’s missing younger brother, Robeson Quatermain, is alive and living there. Dumont also mutters something about Hudson and Trumond, two of Quatermain’s friends who were always in search of adventure and never worried about danger. Quatermain tells Jesse that Hudson and Trumond are rumored to have gone in search of a great lost city where a tribe of white people lived. That night, the two masked tribesmen break into the house and kill Dumont with a knife. Examining a gold coin they find among Dumont’s things, Jesse notes that it has Egyptian symbols but a Phoenician inscription. Quatermain postpones the wedding trip to rescue his brother and friends. In town, he finds his old friend, Umslopogaas, who agrees to go on the expedition with him. Quatermain’s friend, Reverend McKenzie, known as the “Dutchman,” helps assemble a team of five native Askari warriors, and a spiritual guru, Swarma, to accompany them on the expedition. Although angry about the wedding being postponed, Jesse realizes how important the mission is to her fiancé and accompanies him. The group journeys into the mountains, then finds a walled area across the desert. The walls are covered in Egyptian symbols and Phoenician inscriptions and eventually lead to the Tana River. They take canoes downriver, but along the way a native tribe attempts to stop them. Umslopogaas convinces the natives to let them pass, but further downriver, another tribe seems ready to torch their canoes. Quatermain fires his gun and scares them away. The river flows into a cave where a whirlpool almost capsizes the boats. Further into the cave, the water becomes boiling hot in an area called “The Devil’s Heart.” An underground volcano explosion causes flames to erupt from the water, but Quatermain shoots his gun at a stalactite, causing it to fall into the water and the resulting wave pushes the canoes away from the fire. When the river comes to an end, they follow a path through the cave, but Jesse falls into a hole where she finds many dead bodies and many blocks of gold. Quatermain recognizes one of the bodies as his friend Trumond. As they crawl out of the hole, giant snakes attack, but Umslopogaas kills them with his axe. Several of the Askari tribesmen are killed along the way, leaving only Quatermain, Jesse, Umslopogaas, and Swarma alive by the time they emerge from the cave near a waterfall. From the mountaintop, they see a road that seems to be paved in gold and a city in the distance. At the gate to the city, a young white boy comes out, but is attacked by a lion. Quatermain shoots and kills the lion. As the people of the city come to greet the visitors, Quatermain sees they are black and white people living in harmony. The people present the expedition survivors with a feast of tropical fruits. Soon, Quatermain is reunited with his younger brother, Robeson Quatermain. However, the festivities end when high priest Agon appears, announcing that Quatermain committed sacrilege by killing a sacred lion. The city’s two queens, sisters Sorais, who is feared by the people, and Nyleptha, who is beloved, come into the temple. The floor opens to reveal a pit with a giant gold smelter deep below the city. Jesse falls into the pit, but Quatermain grabs her and pulls her to safety. Agon throws a weapon at Quatermain, but it bounces off his chest because he is wearing a special flexible armor tunic underneath his shirt. The city’s people decide main must be a God since he can withstand the weapon. Queen Nyleptha welcomes Quatermain and the expedition, saying they are free to roam the city. Robeson Quatermain reports the city was a paradise until Agon showed up a few years ago. Agon was a slave trader selling arms to nearby natives, the savage Eshowe tribe. Agon preyed on the fears of the people and created a cult of lion gods, slavery, and human sacrifice. The gold smelter is off limits to everyone except Agon, who smuggles out gold using the Eshowe tribesmen. In the gold smelter, Agon has slaves create gold bars and figurines. Anyone who disobeys Agon’s orders is killed, then dipped into the gold and transformed into a statue. Jesse wants to study the city and its culture, but Agon and evil queen Sorais want her and the other visitors gone so they can take over. Agon stirs up the Eshowe and plans to attack the city. Quatermain worries they do not have weapons enough to fend off the attack, but seeing the gold smelter, he realizes they can create many weapons. As the Eshowe attack the city gates, the people drop gold bricks on their heads. The tribe continues attacking and eventually breaks down the gate and rushes inside the city. Quatermain tells the residents to retreat to the temple for safety, then goes to the temple roof when it begins to rain. He hits the roof with an axe to create a lightning rod. As lightning strikes the axe, the gold covering the roof turns to liquid and drips onto Agon and the Eshowe tribe below. They are covered in gold and transformed into statues, With the city safe, Quatermain and Jesse say they are ready for another adventure and kiss.