Walter Hartright, a young drawing teacher who lives in London, needs a job and an escape from the city for the autumn months. One night he goes to visit his mother and sister, Sarah, and is surprised to find his friend Professor Pesca, a cheerful Italian whom Walter once saved from drowning, waiting for him at the Hartright’s family home. Pesca tells Walter that he has found a job for him teaching art to a pair of young ladies in Cumberland, at a place called Limmeridge House, in the employment of a man named Mr. Fairlie. Walter is somewhat uneasy about the job but accepts.
On his last night in London, Walter visits his mother’s house to say goodbye and walks home across Hampstead Heath. On the road he meets a young woman dressed head to toe in white clothes. She asks him the way to London and walks with Walter to the city. On the way, she asks Walter if he knows many powerful men there, and mutters something about a certain Baronet. Walter tells her he is only a drawing master and does not know anyone of rank. He tells her that he has just taken a job at Limmeridge House and is surprised to learn that the woman has been there and that she speaks fondly of the late Mrs. Fairlie. The woman asks Walter if he will help her find a cab once they get to the city; Walter agrees, and he finds one quickly when they reach London. As the cab drives off, another carriage passes Walter, and the man inside leans out and shouts to a nearby policeman. He asks him if he has seen “a woman in white,” as this woman has recently “escaped from an asylum.”
Walter travels to Limmeridge House to start his job. He does not like Mr. Fairlie, who is a pretentious man, but gets on well with his pupils, Marian Halcombe and Laura Fairlie. Immediately, Walter notices that Laura reminds him of someone. He also tells Marian about the woman in white, as Marian is the late Mrs. Fairlie’s daughter, and Marian looks through her mother’s letters to see if she can find any reference to this woman. One night, when Walter and Marian are in the drawing room and Laura is outside, Marian discovers that one of her mother’s letters describes a little girl who came to the school at Limmeridge, where Mrs. Fairlie taught. Mrs. Fairlie’s letter notes that she thought this girl, Anne Catherick, was strange but very sweet and gave her some white dresses to wear. At this moment, Laura comes inside from the garden, and Walter suddenly realizes that Laura looks like the mysterious woman in white.
Walter and Laura begin to fall in love. This seems to make Laura very sad, and one day, Marian takes Walter aside and tells him that Laura is engaged to marry a Baronet named Sir Percival Glyde. She kindly tells Walter that he should leave Limmeridge because Sir Percival is expected to arrive in the next few days to make plans for the wedding. Walter is heartbroken but reluctantly agrees. While they are talking, a maid summons Marian back to the house because Laura is very upset—she has received an anonymous letter warning her not to marry Sir Percival. Marian and Walter ask around in the village to see if anyone knows who sent the note, and they discover a woman in white has been seen near Mrs. Fairlie’s grave. Knowing this must be Anne Catherick, Walter decides to hide in the churchyard that night so he can speak to her if she comes back to Mrs. Fairlie’s grave. His plan works, and he manages to speak with Anne, but she becomes extremely angry when Walter mentions Sir Percival’s name. Unable to calm her, Walter leaves Anne with her companion, an older woman named Mrs. Clements, and the next day he returns to London.
Sir Percival Glyde comes to Limmeridge House to arrange his wedding. Laura is reluctant to marry him, but she has promised her father on his deathbed and feels too guilty to break the engagement. Sir Percival seems charming and considerate, but Marian still does not like him. She finds him bad tempered with the servants, and Laura’s friendly dog always barks at him, which seems to be a measure of his character. Hoping to get out of the engagement, Laura tells Sir Percival that she does not love him, and that she loves someone else, and offers him the chance to break off the engagement; however, Sir Percival delights in her honesty, confesses his undying love for her, and the wedding goes ahead as planned. In the days that follow, Mr. Gilmore, Laura’s lawyer, arranges the marriage settlement. This settlement states that, if Laura dies without an heir, Sir Percival will receive twenty thousand pounds and Limmeridge House, while Laura’s aunt, Madame Fosco, will receive ten thousand pounds. After the wedding, Laura and Sir Percival set off on their honeymoon to Europe, where they plan to meet up with Laura’s aunt and her Italian husband, Count Fosco. Marian arranges to meet the newlyweds on their return at Sir Percival’s house at Blackwater, where she will live with them.
Many months later, Laura and Sir Percival arrive home at Blackwater with Sir Percival’s friend Count Fosco and his wife. Marian and Laura both deeply dislike the Count and are very afraid of him. His wife behaves suspiciously too and submissively does everything the Count says. Marian also finds that Sir Percival’s demeanor has completely changed; instead of the charming (albeit off-putting) man who sauntered around Limmeridge declaring his undying love for Laura, Sir Percival is now extremely irritable and bad tempered, especially toward his new wife. At one point, he tries to force Laura to sign a document without telling her what it is (he has folded the paper so that only the signature line is visible), and becomes aggressive when Laura refuses to sign. Sir Percival’s combative mood is made worse when he hears that Anne Catherick is in the area, and he becomes determined to find her. One day, on a walk to the boathouse near the lake in the grounds, Laura meets Anne Catherick, who tells her that she knows a secret about Sir Percival. Laura agrees to meet Anne the next day. When she tries, however, Sir Percival follows her, drags her home, and locks her in her room. He tries to force her to sign the document again but Count Fosco stops him. Meanwhile, Marian has become deeply suspicious about Sir Percival and Count Fosco’s motives towards her sister. She tries to write to Mr. Fairlie and Mr. Kyrle (the girls’ new lawyer) for help on several occasions, but Madame Fosco intercepts the letters. One night, Marian overhears Sir Percival and Count Fosco in the garden and hears them discuss plan to murder Laura for her fortune. Unfortunately, Marian gets soaked in a rain shower while crouching on the roof to listen and becomes ill with typhus.
While Marian is ill, Count Fosco and Sir Percival continue their hunt for Anne Catherick. One day, the housekeeper, Mrs. Michelson, sees Count Fosco come in from a walk and Sir Percival asks if he has found her, at which Count Fosco smiles. Sir Percival sends Mrs. Michelson away to look at seaside houses for him to rent and, when she returns, she is told that Marian has been sent to Limmeridge, and that Laura will follow suit the next day. All the servants are to be dismissed, and the house is to be shut up. Mrs. Michelson is shocked but takes Laura to the station and sees her off on the train to London. When she arrives back at Blackwater, she discovers that Marian is still at the house and that Laura has been tricked. When Laura gets to London, she is taken to stay with Count Fosco, but dies the next day from heart failure.
Several months later, Marian hears that Anne Catherick has been returned to the asylum and goes to visit her to see if she can find out about Sir Percival’s secret. When she arrives, she discovers that it is not Anne in the asylum but Laura, who has been disguised against her will as Anne. Marian breaks her sister out of the asylum, and they return to Limmeridge, but find that everyone there believes that Laura is dead. In the churchyard, where Anne has been buried in Mrs. Fairlie’s tomb, they meet Walter Hartright, who has returned to mourn for the woman he loves.
Marian and Walter move to London, and Walter decides to investigate Sir Percival Glyde to see if he can uncover his secret. He visits Mrs. Clements, and she tells him that it has something to do with his being caught “in the vestry of the church” in Welmingham with Mrs. Catherick. Walter then visits Mrs. Catherick, Anne’s mother, and, when he mentions the vestry to her, can see from her reaction that the secret is in fact hidden there. He goes to Welmingham and finds that the church marriage register has been forged: Sir Percival’s parents were never married, making him an illegitimate child, and he is not a Baronet at all. Walter runs to the nearby village to check this information in the second copy of the marriage register, and the forgery is confirmed. When he returns to the church that night, Walter is startled to find that it is on fire, and that Sir Percival, of all people, is trapped inside. He has accidentally set the church alight while trying to destroy the forgery and is killed in the blaze. After Sir Percival’s death, Mrs. Catherick writes to Walter and tells him that Anne never knew the secret, but that Sir Percival locked her in the asylum just in case she did know it. In the midst of all of this chaos, Walter and Laura marry.
Now that Sir Percival is dead, Walter goes after Count Fosco. He tracks him down one night at the opera and takes Pesca with him to see if Pesca, who was once involved in Italian politics, recognizes the Count. Pesca does not, but the Count recognizes Pesca instantly and flees the opera house in fear. He is followed by a foreign man who had been watching Walter and Pesca carefully during the opera. Walter questions Pesca and Pesca confesses that he was a member of a secret political organization in Italy in his youth and suspects that the Count is a traitor to this same organization.
That night, Walter writes Pesca a letter with Count Fosco’s address and tells him to come to this address and kill Count Fosco if he does not hear from Walter before the morning. Walter then goes to the Count’s house and blackmails him into writing a confession of the conspiracy against Laura. The Count agrees to do this if Walter will let him go and intercept the letter to Pesca. The Count then writes a confession which proves that Laura is the real Laura Fairlie, and that Anne Catherick is the woman who died at his house. The Count promptly leaves London, and Walter returns to Laura and Marian with his proof. They can now restore Laura’s identity and prove to her relatives that she is alive. Some months later, Walter gets a job which takes him to Paris. While he is there, he passes the Paris Morgue and sees Count Fosco’s body there. He has been stabbed by the foreign man who saw them at the opera, who is a member of the political organization Count Fosco betrayed. Walter and Laura have a son and, when Mr. Fairlie dies, they move back to Limmeridge House and Walter’s son becomes the heir to the property.