In 1842 in Philadelphia, sailor Michael "Nuggin" Taylor faces trial on allegations that he caused the deaths of nineteen people from the ship William Brown . His trial is witnessed by Barton Woodley, a British secret service agent who intends to come to Michael's defense if the verdict should find against him. In court Michael's story is told: When slaves attack Granley, a renowned slaver and the brutal captain of the Blackbird , his dying command is that seaman Powdah captain the vessel and Michael, a passionate abolitionist and friend of Powdah, keep the ship on course to meet with the slave traders. Michael advises Powdah to steer the ship toward a British patrol vessel in order to keep tabs on them, and along the way, they release the slaves onto the coast. The patrol ship captures the Blackbird , and when Michael and Powdah refuse to reveal what happened to the slaves, they are hanged by their thumbs from the halyard. While they are hanging, Powdah confesses to Michael that although he is a seaman, he is afraid of the water, and is now afraid he will fall into the ocean. In order to save his friend, Michael tells his captors, including Lieutenant Stanley Tarryton, that they will confess. Later, Powdah tries to protect Michael by telling them that although he has worked slaving ships for years, Michael only recently came aboard and did not realize it was a slave ship. The captain is suspicious that the Blackbird was caught so easily and suspects that Michael deliberately steered toward them so they would be captured. In Liverpool, Michael and Powdah are acquitted for their actions, and Woodley, who is out to end slavery, takes an interest in Michael, as every ship Michael has worked on has encountered trouble and has seen the release of its slaves. Unknown to Powdah, Woodley enlists Michael to work for British intelligence and entrap the ring of slavers. At the same time, Tarryton meets with his business partner, Pecora, and they plan to take on Granley's established slave trading route. In order to do this, they immediately purchase the ship William Brown , which is departing the next morning for Philadelphia and Savannah, Georgia, and is considered the fastest packet on the seas. Michael also boards the William Brown at dawn carrying Granley's secret plans, and is met on board by Powdah. Tarryton is suspicious of Michael and is especially hostile when Michael falls in love with his sister Margaret. When Tina, the young daughter of immigrants traveling to the United States, knocks over an oil lamp below deck, a fire breaks out and ignites gunpowder, causing massive explosions. Michael struggles with Tarryton for the plans and knocks Tarryton out. The rest of the ship catches fire, and Powdah finds his girl friend, Babsie, with whom he had only just fallen in love, pinned under a fallen beam just before she dies. As Michael helps people into a lifeboat, Tarryton attacks him, but drowns after they struggle in the water. Bereft, Powdah stays on board to be with Babsie as the ship sinks, and knocks Michael into the lifeboat so he will not stop him. A mast falls into the lifeboat, and when Michael revives, he urges his fellow survivors to hang onto the edges of the boat so that it will not founder. Unfortunately, the boat is overcrowded, and the desperate people are causing it to sink. Michael shoots several people, who fall into the ocean to their death, in order to save the lives of the others. At the trial, Michael clearly feels remorse for the actions he was forced to take, and refuses to defend himself against accusations that he is a slaver. After a violent argument erupts in the courtroom when several of the survivors deny the accusations against Michael, the courtroom is cleared. Woodley suddenly appears to defend Michael and reveals enough evidence in Michael's favor to change the court's initial decision of guilty and call for a retrial. Michael and Margaret then reunite.