Our story beings with Walter Hartright helpfully telling us that he's about to tell us a story. (Glad he gave us that head's up.) Walter actually gathered a lot of testimony and letters from people to tell us a dramatic and totally true story. Cue the Law and Order theme song.
So Walter is an art teacher who lands a gig teaching two sisters how to draw. Before heading out to the sisters' house, he meets a mysterious woman dressed entirely in white who has just escaped from a lunatic asylum.
Walter heads to Limmeridge House, where he promptly becomes BFFs with the older sister, Marian, and falls in love with the younger sister, Laura. Marian and Walter investigate the woman in white, who is named Anne Catherick and who bears a weird resemblance to Laura.
But then Walter has to leave because of his love for Laura, who is already engaged to a dude named Sir Percival Glyde. Walter peaces out and Sir Percival arrives on the scene and woos his Laura some more for good measure. But Anne Catherick sends a letter to Laura prior to her fiancé's arrival. The letter tells Laura to stay away from Sir Percival—he's a creep. Sir Percival also makes some shifty legal demands regarding Laura's inheritance, which the family lawyer doesn't like. Laura hems and haws about everything but finally decides to marry Sir Percival anyway, since she promised her dad she would. Marian is less than pleased with the situation.
Flash-forward to after the wedding. Laura and Sir Percival return from their honeymoon, and Marian comes to live with them at Sir Percival's mansion, Blackwater Park (sounds cheery). Count Fosco, Sir Percival's BFF, and Countess Fosco, Laura's aunt Eleanor, come to stay at the house as well. Things go from bad to worse for the sisters as they are forced to square off against the greedy and crafty Fosco and Percival, both of whom are out for Laura's money.
After a tense few weeks, Marian falls dangerously ill after spying on Fosco and Percival in the rain. (Should've brought that umbrella, Marian.) The two men conspire to get Laura out of the house. Laura abruptly dies at Count Fosco's house while Marian is abandoned at Blackwater Park. Yikes.
Except not. See, Fosco swapped Anne and Laura. In reality it was Anne who died, and Laura was shipped off to Anne's former asylum. But Marian figures out what's what and busts her sister out of the loony bin. The two team up with Walter, who is back from a stint in South America, and go on a crusade to get justice for Laura, who is still presumed dead.
After lots of investigating, Walter learns Sir Percival's big secret: he's an illegitimate child and not the rightful heir to his estate or title. Before Walter can let the world know about this, Sir Percival dies in a fire while trying to stop Walter from investigating things further. One villain down, one to go.
Fosco seems indestructible, but then Walter learns some shady things about his past from his Italian buddy, Pesca. Turns out Fosco is on the lam from a political organization that he screwed over once upon a time. Walter confronts Fosco and gets a detailed written confession from him about everything he and his crony Percival did to Laura and Marian. Fosco runs off, but his former political society finally catches up with him and kills him in Paris.
Meanwhile, Walter and Laura have married and eventually they have a son. Laura's identity is restored, but her money is long gone. Anne Catherick gets a proper burial under her own name. Walter, Laura, baby Walter, and Marian move into Limmeridge house after Laura's uncle dies, and they all live happily ever after.