In a European hotel of the 1920s, a man returns to his room while being shadowed by another man. Before the second man can kill the first, he is shot. The man who does the shooting is Charlie, personal chaperon to Eve Tozer, a rich socialite who is heir to her father's fortune. Charlie has found out that Eve's father's business partner, Bentik, has moved to have her father, who has been missing for years, declared legally dead so he can seize all his assets, leaving Eve broke. Eve resolves to find her father.
Eve is unsuccessful at first in finding someone to fly her to the far reaches of Asia, where her father was last rumored to have gone. She is eventually recommended to a local pilot, Patrick O'Malley, who is a former World War I flying ace. He is also a drunk. When Eve arrives at his airfield, she finds he has two biplanes, one named Dorothy, the other, Lillian (after acting sisters Dorothy and Lillian Gish). O'Malley initially turns down Eve's request, despite her generous offer of money. However, unpredictably, Eve herself is an accomplished pilot, which she proves to O'Malley very quickly by taking him on a rigorous flight in one of his planes. O'Malley accepts her offer and tells his mechanic, Struts, to mount Lewis-type machine guns on both planes since they'll be flying into hostile territory.
As Eve prepares for her trip, and she and Charlie walk down a crowded street, they are attacked by assassins sent by Bentik. Eve escapes but Charlie is killed while seeing she gets away safely. Eve goes immediately to O'Malley's airfield, followed by Bentik's people. She, O'Malley, and Struts manage to escape the thugs sent after Eve and they fly east.
At the end of their journey's first leg is a British airbase in Iraq. That night, O'Malley and Eve go to the officer's club, where O'Malley quickly becomes inebriated. O'Malley is asked about his war record and though he has many victories to speak of, he becomes somber, talking about flying against young, highly inexperienced pilots, who were easy "kills". When Eve tells him they should go to bed early, O'Malley becomes quite rude. The next morning O'Malley is quite hung over, however, they leave on schedule.
The next leg of their journey brings them to a tribal camp in Afghanistan. The camp's leader, the Sulehman Khan, welcomes them, but warns that Eve must be compliant with their laws concerning women, who are treated as subservient. Later, at a banquet, when Eve asks the Khan if he knows her father's whereabouts, he tells her he is dead. However, the Khan has other plans; he wants O'Malley to use one of his planes to drop bombs on a nearby British camp. The Khan's nephew will fly with O'Malley, armed with a pistol in case O'Malley tries to fly off. The Khan also plans to hold Eve and Struts hostage until O'Malley returns. That night, they are met by an enslaved Nepalese woman, Alessa, who says she will help them escape. She also knows that Eve's father was indeed at the Khan's camp and escaped to her village in the Himalayas. Eve and O'Malley promise to take Alessa home.
The next morning, O'Malley takes the Khan's son, with the explosives, into the air on the mission. Once in the air, having not told the Khan's nephew to fasten his lap belt, O'Malley suddenly inverts the plane, dropping the man on the Khan's camp. O'Malley creates a diversion by dropping bombs on the camp while Eve, Struts and Alessa successfully escape in the other plane.
The group arrives in Nepal. When they arrive, Eve, quite exhausted, asks if her father is still there. He is not, and Eve faints. While she suffers from fever and delirium, O'Malley stays with her until she is well several days later. Meanwhile, Bentik learns of his assassins' failure and hires a German flying ace, Von Hess, to track down O'Malley and eliminate him. The next morning, in the midst of an argument (Eve mistakenly believes that O'Malley took advantage of her while she was ill), Von Hess attacks the village, destroying one of O'Malley's planes. O'Malley quickly flies into combat and downs Von Hess after a brief dogfight. Upon landing, O'Malley asks Eve to tell him the truth. Eve tells him that Bentik may have sent the man to kill them. O'Malley is flustered, but agrees to continue. The two talk to the village's shaman, who tells them that Eve's father has gone to the Chinese province of Sinkiang.
Eve and O'Malley leave Struts behind and make the long flight to Sinkiang. In a remote village, they finally find her father, Bradley, who is working with the villagers to defeat a local warlord, General Wong. While Eve settles in, Tozer, while giving the pilot a tour of his defenses, asks O'Malley why they came so far just to find him. O'Malley tells him about Bentik's plans. Tozer laughs, saying that before he left, he arranged for Eve's financial future to be legally bound and that Bentik presents little threat. O'Malley plans to leave with Eve the next day for Hong Kong to file against Bentik in a British court. Eve refuses to leave, saying she wants to stay and help her father. O'Malley says she's crazy and she seems convinced to leave.
The next morning, Wong begins his attack, which Tozer is well prepared for, having mined the valley around his fortress. He gains a special advantage when Eve suddenly appears, flying O'Malley's plane, dropping grenades on enemy positions. She takes out a large cannon, but is hit by machine-gun fire and crashes. O'Malley rides out on horseback to find her. Eve is alive and uninjured, but a nearby enemy squad finds them. While O'Malley fights them off, Tozer begins setting off the mines in the valley, quickly winning the battle and killing Wong in the process. The soldiers retreat and O'Malley and Eve share a romantic moment.