Act I

On Christmas Eve, 1739, 14-year-old John Newton celebrates the holiday with friends (including young Mary Catlett) and family at his seaside home in England. His father, Captain Newton, is away on a sailing voyage. Soon afterwards, John’s mother dies and the gruff Captain Newton expects his son to follow him to sea. Although John wants to study music at a conservatory, he parts from Mary and sails with his father (and his school friend Robert) for several years. Four years later, in 1743, John returns to greet Mary, who is now an aspiring singer, but she finds him a changed young man. He has become immersed in his father’s business as a slave trader. While at the dock, Mary shows compassion to a pregnant slave being offloaded from the ship. A commotion ensues when the slave is kidnapped by a group of hooded men; John is tasked by Major Gray to find and retrieve her. Later that day, Mary is secretly invited to join an abolitionist group. She talks with her own black maidservant about how she became a slave. Mary’s mother encourages her to pursue a relationship with the handsome and aristocratic Major Gray. Mary, John and Gray all attend a ball during which Redcoat soldiers drag in two badly beaten abolitionists and the pregnant slave, also beaten. Major Gray scornfully points out that his soldiers, rather than John and his civil authorities, retrieved the slave. Gray leaves with Mary. The next day, Mary meets with the abolitionists. She agrees to begin a relationship with Major Gray to act as their spy. Meanwhile, John is press-ganged into the Navy, but his father persuades the Navy caption to promote John to the rank of midshipman. At her home, Major Gray proposes to Mary. As a relative of King George II, he must introduce Mary to the King to obtain royal consent to the marriage. Tyler, an emancipated slave who works as an abolitionist, urges that Mary to confront the King publicly about the evils of slavery.

Act II

In the jungle in Sierra Leone, John and his trusty slave Thomas are captured by African warriors and their Princess Peyai, who threatens to kill John. Thomas tells her that John’s father is head of the Royal Africa Company, so she sends a letter to Captain Newton demanding 5000 pounds sterling as ransom. Captain Newton prepares to sail to Sierra Leone, and Mary asks him to give John a letter. Meanwhile, John is now working for Princess Peyai, helping her to break up African families and assign slaves to ships. But the Princess becomes annoyed when Thomas tries to help one of her slaves and sells Thomas as a slave bound for Barbados. Thomas feels betrayed when John does not help him. Captain Newton arrives in Sierra Leone. The Princess refuses to release John, but the Captain shoots one of her warriors. The Princess grabs a dropped pistol and shoots the Captain, and John kills the Princess. John orders his father’s men to burn down the village. On the ship, Captain Newtons wound is infected, and he dies. John finds Mary’s letter, which gives him a change of heart. He sails to Barbados to find Thomas. Mary’s voice teacher, Mr. Whitley, reveals to Major Gray that Mary is working with the abolitionists. Gray captures Mary’s maidservant and threatens to harm her if Mary does anything foolish when meeting the King. Despite his threats, Mary speaks openly to the King and court about her feelings on slavery. She is seized by Major Gray and the Redcoats, as the King and Gray try to quiet her. John and Thomas (now a free man) arrive, and John bolsters Mary’s argument, confessing that he has been guilty of slave trading. He says that he now knows slaves are humans with souls. Mary is overjoyed by John’s conversion, and they reunite.