Marco Polo travels to China, falls in love with Kublai Khan's daughter, and foils the devious plots of the minister of state.
Niccolo Polo shows treasures from China and sends his son Marco Polo (Gary Cooper) there with Binguccio (Ernest Truex). They sail from Venice, are shipwrecked, and cross the desert of Persia and the mountains of Tibet to China. The philosopher Chen Tsu (H. B. Warner) invites them to eat spaghet. Children explode a fire-cracker, and Marco thinks it could be a weapon. Ahmed (Basil Rathbone) advises Emperor Kublai Khan (George Barbier) that his army of a million men can conquer Japan. Kublai Khan promises Princess Kukachin (Sigrid Gurie) to Persia. Marco sees Kukachin praying for a handsome husband. Kublai Khan lets Marco test the maidens with a question, and he selects those saying they did not know. Ahmed shows Marco his private tower with vultures and executes a spy with lions. Kukachin tells Marco that she is going to marry the king of Persia, but he shows her what a kiss is. A guard tells Ahmed. Kublai Khan and Ahmed tell Marco to spy on suspected rebels. Kukachin warns Marco, who hopes to marry her.
Marco is guided to Kaidu (Alan Hale), who executes spies. Marco and Binguccio are captured. Kaidu's wife Nazama (Binnie Barnes) is jealous and gazes at Marco. Kaidu orders Marco to charm his wife. Kublai Khan says good-bye to Kukachin and marches off to war. Bayan (Stanley Fields) tells Ahmed that he killed Marco. Nazama inches closer to Marco, who moves away and examines coal. Ahmed is told that Kublai Khan's army was destroyed. Ahmed takes jewelry from the Persian ambassador and gives it to Kukachin, who must marry him. She sends a message to Marco by bird; but Kaidu warns Marco not to escape.
Kublai Khan returns to Beijing, and Ahmed tells him to sign his will, making Ahmed his heir. Kublai Khan refuses until he sees Kukachin with the vultures. Marco urges Ahmed's man Toctai (Harold Huber) to kill Kaidu after he has detained him with Binguccio's singing; but Marco saves Kaidu's life, and Toctai is captured. Kaidu tells Marco he resents Kublai Khan's taxes. Marco urges Kaidu to attack Ahmed while the army is gone and rushes away from Nazama. Marco goes to Chen Tsu for fire-powder that was ordered by Ahmed. Marco sneaks into the palace as a servant washing the floor and prevents Kukachin from stabbing herself. Kaidu's forces enter the city as Marco runs out of the palace before the gate closes. While Ahmed is wedding delaying Kukachin, Marco uses the fire-powder to blow open the gate. Marco comes in and fights Ahmed, pushing him into the lions' den. In the final scene Kublai Khan assures Kaidu the injustice has ended, and Marco offers to take Kukachin to Persia.
Threads using historical men have been woven into an adventure story, but the romance is film fantasy. Ahmad was governor of Beijing for 22 years and used his power to execute people without trial in order to gain wealth and have his way with women until he was assassinated. Also there were conflicts between Kublai Khan and Turkestan king Kaidu.