Season 1:
Lynn Russell is a 5-year-old girl of mixed ancestry. Her mother, Misuzu, is an ordinary commoner from Japan and her father, George, is an Englishman from an aristocratic family. Having been born and raised in Japan until she was 5, Lynn is eventually taken to England by her mother. However, she falls victim to a car accident, while Lynn survives with minor injuries.George arrives to the hospital to see Lynn and can't bring himself to tell her Misuzu died. She is taken to his house, the Marble Mansion, and is also told she has a sister from George's first marriage named Sarah. At first, Sarah wants nothing to do with Lynn. She is used to being lonely and also believes that Lynn will take what little attention George gives her (due to being a workaholic). Though Sarah is often cruel to her, she eventually accepts her friendship after Lynn goes out of her way to still be kind to her despite her initial rejections.
Lynn also befriends the Brightons, two boys who's house neighbours the Russells. After seeing the elder Brighton, Arthur, ride a White Stallion named Alexandra, Lynn develops a passion for the same thing. She and Arthur often go on horse rides, and she begins to fall for him, while being oblivious to the younger Brighton, Edward's, feelings for her.
Lynn eventually finds out her mother died when Madeleine Waverly, a wealthy noblewoman who George's father has arranged to be his fiancee, bluntly says so after declaring her intent to be George's new wife. Lynn is heartbroken and doesn't believe it, but Sarah is forced to tell her the truth. Madeleine eventually moves in to the Marble Mansion and becomes an authority there, as George's father Duke Warbawn has arranged for her to be his fiancee. The Russell family has been on the verge of poverty for some time and Madeleine has enough money to pay off their debts. Duke Warbawn has also never liked Lynn due to being the child of a foreigner and preferred her older sister Sarah; he hopes George will send her back to Japan and excommunicate her from the family.
Madeleine covets George's noble title, and blames Lynn for George's reluctance to marry her. She goes out of her way to punish her while also excusing her two children, Thomas and Mary, frequently bullying Lynn. Lynn manages to overcome it thanks to the support of Sarah, the Brightons and the house staff. She also swears to be a Proper Lady, just like her mother wanted her to be.
Lynn and Sarah become closer as they spend more time together. Lynn also notices Arthur's feelings for Sarah, so she turns her feelings to Edward. When the Russells make a trip to visit Duke Warbawn, he welcomes George and Sarah while rejecting Lynn. His sister Isabelle, on the other hand, takes a shine to her and urges him to change his mind.
One day, Lynn overhears Sarah and George talking. Sarah angrily asks George why he agreed to marry Madeleine, and George admits that his father offered to finally accept Lynn into the family if he did so. Horrified at the thought of the cruel Madeleine becoming her and Sarah's stepmother, Lynn tries to flee back to Japan. She tearfully admits this to Alexandra, before running to pack her things. Edward overhears this and tells Arthur, and together they manage to reach the airport and stop Lynn from leaving. George sees how distressed Lynn and Sarah are, and swears he won't marry Madeleine and that the two girls are of the most importance to him.
Season 2
It has been three years and Lynn is now 8. Because the Russells failed to pay their debts, they lost the Marble Mansion - Sarah now lives with Duke Warbawn and Lynn lives with great-aunt Isabelle. The two sisters sorely miss each other and wish to reunite, but things are looking glum as George has had no luck recovering his wealth so far. The Duke also bars Sarah from seeing Lynn, and she has to ask for special permission to do so.Saint Patrick's Academy announces that like every year, they will bestow the Lady's Crest award to the student that brings the school the most honour. Lynn hopes to win it and decides to pursue a career in equestrian sports. Isabelle buys her a horse, Andrews, who was about to be put down by his old owner Vivian. Lynn and Andrews train together and she helps him overcome his trauma of being abused in the past. Many note Lynn's potential, and suggest that she try to represent Great Britain in the Olympics.
The Waverlys have since departed from England to Switzerland, accepting that George has ended his relationship with their mother. However, Mary wants toMadeleine and her two children have since departed from England and live in Switzerland. Mary, still bitter that George rejected her mother, decides to seek revenge on the Russells. She decides to go to England on her own, asking her grandfather Victor Reynolds to enroll her in Saint Patrick's Academy. Reynolds does so, asking the daughter of his friend to house Mary. The daughter of his friend turns out to be Vivian, the very same person who Andrews used to belong to. Vivian and Mary bond over a mutual hatred of Lynn (Vivian sees her a rival for the Lady's Crest and Mary has hated her ever since they first met) so they work to sabotage her. However, Mary suddenly betrays Vivian and hopes to win the Lady's Crest for herself, so she turns the sabotage on Vivian and cuts the reins of her horse during a race. Vivian ends up badly injured and loses the ability to ride. However, she is not angry at Lynn, knowing that the girl is too good-hearted to do something so underhanded to her. Despite this, Lynn is blamed for what happened and disqualified as a candidate for the Lady's Crest.
Lynn's friends work on gathering evidence to clear Lynn's name, with Vivian's help. Vivian asks her father to grant a loan to the Russells, and also tells him what Mary did to her. Edward presents the slashed reins to Victor Reynolds and insists on Lynn's innocence. Victor is reluctant to believe Edward and Mr. Spencer at first, because he loves his granddaughter. However, after Mary acts rudely to Lynn in public, he changes his mind. He also makes a deal with Lynn - if she wins the race for the Olympic qualifier, he'll grant the Russells a loan that will clear their debts. Hearing this, Lynn agrees.
Mary prepares to go back to Switzerland, having lost the chance to win the Lady's Crest after being beaten in a tennis match by Cathy. However, Reynolds prevents her and confronts her with the allegations. He forcibly drags Mary to the race, where Lynn competes against many other candidates. All the friends Lynn's made along the way arrive to support her, including Duke Warbawn. Sarah and Isabelle are surprised to see him there but he confesses that he may have been wrong about Lynn.
Lynn wins the race with Andrews and earns the Lady's Crest. Duke Warbawn greets her and finally acknowledges her as his grandchild. Reynolds grants the Russells a loan, and they earn their home back. He also tells Mary that she is going to be severely punished and hauls her off.
At the Marble Mansion, George gives Lynn a box and says that Misuzu wanted her to have it. She opens it with the key Misuzu gave her earlier and finds a tiara in it. As she puts it on, she has an Imagine Spot of her and Sarah as princesses riding carriages, with Edward and Arthur as their respective knights, as the boys have since confessed their love for them. Lynn then breaks the fourth wall and thanks the viewer for watching, saying that from now on she will still strive to be a true Lady.
