At the request of her dying father, heiress Laura Fairlie marries Sir Percival Glyde, despite her love for Walter Hartridge and the warnings of Ann Catherick, a half-witted girl who bears a striking resemblance to Laura. After the marriage, Glyde schemes to appropriate his wife's money. When he learns that Ann has escaped from an asylum and has perished, Glyde takes Laura to the asylum and commits her, claiming that she is Ann. He then informs everyone that his wife had died, and buries the body of the insane woman in her place. Walter and Laura's half sister, Marian Halcombe, become suspicious, however, and remembering Ann's previous warnings, discover what Glyde has done. After Glyde meets his death in a fire, Walter rescues Laura and the two lovers are reunited.