An experienced seaman believed to be a slaver is tried after many die in a sea disaster.
Based on a true story, in 1842 a prosecutor (Porter Hall) accuses slaver Michael Taylor (Gary Cooper) of being responsible for 19 deaths at sea; but George Martin (Robert Cummings) and others argue that he saved their lives. Yet the jury finds Taylor guilty. Then Barton Woodley (George Zucco) for England's government tells the judge what actually happened.
On a slave ship Taylor wakes his friend Powdah (George Raft) from a nightmare. Slaves are whipped by the captain and attack him. The dying captain turns the ship over to Powdah and dies. Taylor gets Powdah to alter course toward the patrol ships. Taylor and Powdah are hanged by their thumbs for dumping the slaves overboard. Powdah says he let Taylor be in charge, and Taylor says he let 600 slaves swim ashore. Lt. Stanley Tarryton (Henry Wilcoxon) apologizes to Taylor and Powdah.
At Liverpool Woodley tells an official that Taylor has helped slaves escape before. Powdah and Taylor are released and drink beer. Woodley asks Taylor to help him destroy the slave trade, and he agrees. Lt. Tarryton tells a wealthy man to buy a ship he can take to Savannah. Woodley tells Taylor that he must be known as a slaver. Taylor can't find Powdah and leaves him a note. Taylor helps Margaret Tarryton (Frances Dee) on a muddy street.
Margaret asks her brother Lt. Tarryton why he is going to America, and he is told to take her along so she won't talk. Taylor finds Powdah in his cabin. A lady's maid Babsie (Olympe Bradne) befriends Margaret and loans her a dress. Powdah drops cards in order to meet Babsie. Taylor gives Margaret a remedy for nausea; but Lt. Tarryton calls Taylor a slaver. Taylor recites poetry, and Margaret thanks him. They dance. The captain (Harry Carey) invites them to his table, and Lt. Tarryton asks Taylor about slaving. Powdah tells Margaret that Taylor is not a slaver, but Powdah was. Taylor kisses Margaret.
A fire starts below. Lt. Tarryton holds a gun on Taylor and asks where he got the letter. Taylor knocks down Tarryton as the fire spreads, causing explosions. Taylor takes the letter and saves Margaret. Some people drown. Babsie's legs are crushed, and Powdah tries to save her; but she dies. Taylor gets a boat and stops panic. George Martin knocks away Tarryton's gun. Tarryton hits Taylor, who fights and kills Tarryton. Margaret tells Taylor she hates him. Taylor tells Powdah to get in the boat; but Powdah says the boat is too full and knocks Taylor out and into the boat. Powdah puts his ring on dead Babsie's finger as the ship sinks. Taylor wakes and takes charge of the damaged and overcrowded boat. When the boat starts to sink, Taylor shoots some people, who were pulling it down.
Woodley concludes his appeal for Taylor and shakes his hand. The prosecutor asks for a new trial, and Margaret gives Taylor a flower.
This romantic adventure story portrays the greedy motives behind the infamous slave trade and explores the irony of a man trying to stop it having to share its horrible reputation.