The beginning of the film moves very quickly. Text tells us that it is 1769; England is still a slave economy. Captain Sir John Lindsay (Matthew Goode) navigates through a slum. He has come to retrieve his young, biracial daughter, Dido Elizabeth Belle, whose mother, a slave, has died. Though this is the first time they have met, he earns her trust by offering her some candy, and tells her he is taking her to the life she was born to. He brings her to the home of his uncle, Lord Mansfield (Tom Wilkinson), the highest judge in the land, who lives there with his wife, Lady Mansfield (Emily Watson), spinster sister, Lady Mary Murray (Penelope Wilton), and their niece, Elizabeth Murray, who they are fostering now that her father has remarried. Though the Mansfields are shocked that Lindsay's child is black, he convinces them that it is her right, as a Lindsay, to live at the family estate. Once they agree, he tearfully says goodbye to Dido, as he is bound on a long voyage. He tells her to remember how much she is loved.
Dido meets her cousin Elizabeth, who is very curious and loves to tease their aunt Lady Mary. Lord Mansfield joins her in the portrait gallery, where she sees the painting of an ancestor with a black servant staring up at him. She doesn't like what she sees. Later, she and Elizabeth play together while Lord and Lady Mansfield watch. Lord Mansfield says that they have needed a companion for Elizabeth, and Lady Mansfield says that that is what they will tell people, though her husband points out that Dido's lineage gives her the right to be here. Lady Mansfield asks whether they are to rate her blackness above or below her noble blood, and wonders what will happen when the Mansfields are no longer there to protect her. For most women would marry, but they fear that anyone willing to overlook her race would demean her. They also worry about the prospects of Elizabeth, whose father has basically abandoned her.
Quickly, ten years have passed, and Dido (Gugu Mbatha-Raw) and Elizabeth (Sarah Gadon) have grown into young women and the best of friends. One day, Lord Mansfield delivers bad news to Dido: her father, whom she never saw again after their first meeting, has died. However, he has also left her a substantial inheritance, making her an heiress and suddenly a valuable marriage prospect. She is stunned by the news, and Elizabeth is excited for her, even though her own future (having been basically disinherited by her own father in favor of his new family) is very insecure. The Mansfields decide to throw a dinner party, hoping to find a young man interested in Elizabeth. Dido is pleased, until she is reminded that, while she dines with the family when they are alone, it is not "proper" for her to be at a formal dinner. She can, however, sit with them as they relax after dinner. That night, Lady Ashcroft (Miranda Richardson) and her sons James (Tom Felton) and Oliver (James Norton) come to dinner. The mother and eldest son, James, are clearly very racist and only interested in finding a rich wife. At dinner, Lady Ashcroft pesters Lord Mansfield about a case he is hearing in court, about a ship called the Zong, but he will not talk about it.
Meanwhile, Dido is walking through the grounds while she waits for everyone to finish dinner. She is startled by a noise and rushes back to the house. Moments later, the young man who startled her, John Davinier (Sam Reid), arrives with a message for Lord Mansfield from his father. Dido, still startled, is very rude to him and he leaves. Finally, the guests finish dinner and meet Dido in the drawing room. Lady Ashcroft and James are horrified by her, but Oliver finds her exotic and interesting. And when he tells his mother about Dido's inheritance, she is suddenly much more willing to have a black daughter-in-law. Elizabeth, meanwhile, has become totally smitten with James.
The next day, Dido goes to fetch some books from her uncle's study, only to find him talking with Davinier, the man from the previous night. It turns out he wants to apprentice under Lord Mansfield as a lawyer; as the son of a poor parish curate, he cannot afford to set himself up. He speaks passionately about wanting to change England for social justice. Lord Mansfield is unconvinced and he asks Dido what she thinks. She apparently speaks highly of him, despite their previous encounter, because we see him seek her out later to thank her. She is still distant, but clearly intrigued by his passion. However, they have another misunderstanding and argue again. Later, Dido discovers that her uncle has commissioned a painter to do a portrait of herself and Elizabeth. She is very upset--the only paintings she has seen of a black person shows them much below a white person--but he insists. As they sit for the painter, she and Elizabeth talk about James and Oliver Ashcroft. Dido once again hears mention of the Zong case her uncle is trying, but no one will tell her about it.
Leaving another sitting a few days later, she runs into Mr. Davinier. She asks him to tell her about the Zong. He is shocked no one in the house has told her. The Zong was a slave ship that threw its slaves overboard, still alive and chained, citing that it did not have enough water for both the sailors and the slaves. The insurance company is refusing to pay for the lost "cargo" and Lord Mansfield is hearing the case. (This, by the way, is an absolutely true story). Dido is horrified by this, and he agrees with her. Later, she confronts her uncle about the case, but he insists there are many angles and is angry that someone told her. He angrily dismisses Davinier as his student, especially after he seems to suggest that he would like to marry Dido (their attraction has been obviously growing). Dido is sad to discover Davinier has left without saying goodbye.
Some time later, Lord and Lady Mansfield take Dido and Elizabeth into separate rooms to tell them something. The family will be going to London soon. The girls are overjoyed; this means they will be "coming out" as official marriage prospects. But this is not the case, they are told. Elizabeth will have her coming out, but Dido will not. Lord Mansfield basically tells Dido that any man who would overlook her race to marry her would just be after her fortune and would not be good to her. He shows her the keys to the household and asks her to take them when they return. Dido is horrified; the keys belong to her spinster aunt, Lady Mary, and she is not ready to resign herself to that life. When Elizabeth and Dido see each other again, they embrace and Elizabeth tells Dido she is so sorry.
When they get to London, they meet again with Lady Ashcroft and her sons. Oliver asks Dido if she would like to step out with him to Vauxhall Gardens. James says it wouldn't be appropriate, but Dido agrees just to spite him. That night at the gardens, James continues to charm Elizabeth, though it is clear he is only interested in the money he thinks she will inherit. When Lady Ashcroft speaks of this to Lady Mansfield and Lady Mary, they are forced to reveal the truth, that Elizabeth will have no dowry. Meanwhile, Oliver and Dido grow close, until he begins to talk about how much he loves her despite her race and origins. She is obviously hurt, but tries to hide it. Suddenly, she recognizes Mr. Davinier in the crowd. She slips away from Oliver and goes to speak with him. He tells her he has now joined a group of young men trying to spread information about the Zong case, with the hope that, should Lord Mansfield rule against the traders, it will strike a blow to the trade in England. He tells her where he is staying, if she ever would like to meet him. They are both very happy to see each other again.
Since he learned of her poverty, James has stopped visiting Elizabeth, who still believes he loves her. Oliver, however, continues to court Dido, even as she begins to secretly visit Mr. Davinier, to help him with his cause. Eventually, Oliver proposes to Dido, who is taken aback but agrees. Elizabeth, though, is crestfallen that Dido, who--with her fortune--did not even need to marry, has secured a husband and Elizabeth has not. Still, the girls remain friends. After her engagement, Dido sees Mr. Davinier again to tell him, and talks about how she realizes she has been doubly blessed with freedom: as a black person in a slave nation, and as a woman with the income not to need a husband. However, she says, she would still like to have a marriage of equals, where she and her husband can be partners. She talks about how little she knows of her mother, except for the color of her skin. Davinier responds, "You also know she was beautiful"--a very different response from Oliver's talking about overlooking her heritage.
Dido decides to sneak into her uncle's office to see if she can find any evidence for Davinier. What she discovers, and shows him, is a map of the Zong's route that her uncle has marked with all the places they failed to replenish their water supply. This proves that the slavers were negligent, and that they knew their diseased slaves would be worth more dead and insured than sold on the market. Later, at a garden party, James Ashcroft corners Dido, and tells her he will never accept her as his sister-in-law. He reveals how little he cares for Elizabeth, and shows his disdain by grabbing Dido's arm and shoving his hand under her dress. She is sickened by him. Later, when she tries to tell Elizabeth about it, her cousin refuses to believe her, and they fight for the first time. Lord Mansfield has also discovered that Dido has been visiting Davinier, and he confronts the two of them. Davinier expresses his love for Dido, but Mansfield said that, as a poor curate's son, he could never marry her. Dido is furious and disappointed with her uncle, both for his treatment of Davinier and the possibility that he will rule for the slavers in the case. She softens, a little, though, when he shows her the finished portrait he commissioned: she and Elizabeth have been painted side by side, as equals. (We do see Lord Mansfield talking to a colleague about the case; his problem seems to be that, while he knows the slavers are in the wrong and that slavery is morally wrong, he worries that his ruling against them, as the highest judge in the country, might cripple the nation's economy).
Dido chooses to break off her engagement to Oliver, who is saddened but understands, and Elizabeth learns of James's treachery when she reads of his marriage to another woman in the newspaper. The girls reconcile. Finally, the day for Lord Mansfield to give his verdict arrives. Both Dido and Davinier are in the audience. At first it seems as though he will acquit the slavers, but eventually he condemns them and the whole practice of slavery. Dido and Davinier are overjoyed. They meet Lord Mansfield outside the courthouse, where he tells them that he will again take Davinier on as his apprentice, which will give him the income to marry Dido. They embrace and kiss. Text tells us that Lord Mansfield's ruling in the Zong case marked the beginning of the end of slavery in England, that Dido and Davinier married, and that Elizabeth too eventually became a wife and mother. It ends with the real portrait of Dido and Elizabeth.
You can send in your spoiler to other movies by going here.