Saharan guide, Joe January (John Wayne), is stuck living in Timbuktu due to debts owed to a corrupt Prefect named Dukas. When Paul Bonnard comes to town in need of a guide for a mysterious expedition, Dukas introduces him to Joe.
Joe only agrees to the job as it will allow him to pay off his debt to Dukas, and get out of Timbuktu. As the men set out, we quickly learn that Paul is obsessed with his father’s disappearance over a treasure he found at a lost city in the middle of the Saharan Desert.
The night before they leave, Paul charms a disreputable woman named Dita. She quickly developes a crush on him because he looks past her seedy live she’s lived. Dita tries to join the expedition, but Joe refuses due to them not having adequate supplies for her. However, on the first day, Dita hitches a ride with a local caravan who drop her off on the two men’s journey.
Along the way, tensions mount as the men both fall for Dita, and Dita falls for both of them. As their water supply dwindles, Joe wants to turn around, but when he and Paul argue about it, Dita dumps out the little water they have because she believes Paul when he says his father wrote about an oasis by some white cliffs which leads to the lost city.
Now, with no other choice, the three press on, and they do find the oasis as Paul’s father wrote. They also find the lost city nearby which turns out to be an ancient Roman city. In the middle of the ruins, They find three skeletons belonging to Paul’s father, his guide, and a woman.
They are able to surmise from the evidence that Paul’s father killed his guide and the woman after finding them in each other’s arms, and he then killed himself. However, there’s no sign of the lost treasure. The harsh reality about his father shatter’s Paul, and he does something he’s never done before; get drunk.
Meanwhile, Joe goes looking for clues about the treasure, and finds Paul’s father’s bible. Using clues from a page whose corner was folded over, they find the treasure in an underground aqueduct filled with bats. They clean all the bat guano off the treasure, and prepare to leave the next morning.
During the night, Paul tries to make sweet, sweet love to Dita, and she rebukes him. Paul snaps, and thinking she and Joe will steal his treasure while he sleeps, he shoots at the two, and runs off. Joe and Dita hide out for the rest of the night only to find Paul’s left with all the donkeys, supplies, water, and treasure; leaving them for dead.
However, Joe know his donkeys, and he figures they can catch up to Paul, so they head out after him on foot. When they finally catch up to him, all three are near death from dehydration. Paul is unconscious, and all his water is gone.
Joe sees one of his donkeys digging, and figures water is only about 10 feet down, so he and Dita start digging for it. Paul regains consciousness just long enough to figure the two are digging his grave. He buries the treasure, and then musters enough strength to stab Joe in the back with a large knife. Dita shoots Paul; killing him.
With Joe near death himself, Dita spots a caravan in the distance, and flags them down. Relieved that the caravan is not an oasis, the two appear to survive the ordeal (without the treasure).