The Woman in White is presented as a series of documents, including testimony, letters and diary entries. The primary narrator is 28-year-old drawing tutor Walter Hartright, who is commissioned to tutor two young ladies at Limmeridge House in Cumberland. The night before embarking on his journey, he encounters a stranger on a lonely road. The woman, dressed all in white, alludes to her links with Limmeridge House and the Fairlie family. She conceals her identity, but mentions an intense hatred of a certain baronet. Minutes after she slips away, Walter discovers that she has escaped from an asylum for the insane. He has a foreboding that this won’t be the last he hears of the woman in white.
Walter arrives in Cumberland, and is charmed by his students: wise and kind Marian Halcombe, and her half-sister, dreamy, beautiful Laura Fairlie. As the months pass, he realises to his dismay that he is in love with Laura, and that she returns his feelings. Laura is however engaged to a baronet, an arrangement made by her father prior to his death. To avert social disaster, Walter must leave Cumberland.
Before he can do so, the mysterious woman in white reappears. Walter and Marian undertake some detective work, and find out that she is Anne Catherick. Walter realises that she is the author of an ominous letter to Laura warning of the evil that will befall her if she marries Sir Percival Glyde. But before Walter and Marian can work out why Anne penned the letter, or investigate her uncanny resemblance to Laura, Anne disappears.
Walter returns to London. Laura and Sir Percival are married, despite the bride’s reluctance. Walter finds himself relentlessly followed and spied upon. With Marian’s help, he secures a commission to travel to South America, where he hopes to escape his heartbreak and his stalkers.
Laura, Sir Percival and Marian settle in Hampshire, at Percival’s dilapidated estate. They are joined by an Italian Count, Fosco, and his wife. The Count is a somewhat sinister presence, and he has Percival firmly in his power. Percival makes it clear that he married Laura for her money, and that he intends to get it all, without delay. With the sisters’ situation looking increasingly desperate, Anne Catherick reappears and promises to reveal a dreadful secret about Sir Percival. Marian, however, falls gravely ill and Anne disappears again. When Marian recovers, she is told that Laura has died.
As events unfold, however, it emerges that Percival and Fosco have contrived to switch the identities of Laura and Anne: Anne has died, allowing Percival to inherit Laura’s money, while Laura has been incarcerated in the asylum. Marian stumbles across the truth, and she helps Laura escape from the asylum. This daring rescue coincides with Walter’s return to England. By chance, the three are reunited.
Walter resolves to make Percival and Fosco pay for their crimes, and to restore Laura’s identity under law. He and Marian set out to uncover Percival’s dreadful secret. Walter eventually discovers that Percival is illegitimate – he has falsely claimed his title and inheritance. Percival, trying to destroy the evidence of his crime, dies in a fire. Walter and Laura are able to marry.
Fosco is now the only person who can officially verify Laura’s identity. Walter discovers that he, too, has a deadly secret, and he forces him to provide the proof he needs to assist Laura. Fosco flees England and is later murdered. Laura’s true identity is officially recognised, and eventually she, Walter and Marian return to Limmeridge house.