Belinda is a young lady who lives with her aunt, Mrs. Stanhope. Being unwed, Belinda is sent to live with Lady Delacour, whom Belinda considers fascinating and charming. Lady Delacour believes herself to be dying of breast cancer. She hides her emotional distress caused by her impending death and poor relationships with her family from Belinda through wit and charm. The first half of the novel is concerned with the blooming friendship between Belinda and Lady Delacour, which is broken by Lady Delacour's fear that Belinda plans to marry Lord Delacour, expressed in the line, "I see...that she [Belinda] who I thought had the noblest of souls has the meanest! I see that she is incapable of feeling."
Belinda subsequently moves to the home of the Percival family, the embodiment of the ideal family. Once Lady Delacour seeks treatment for her illness, Belinda returns to support her. Upon her visit to the doctor, Lady Delacour discovers her disease is not terminal and reconciles herself with Belinda. She eventually makes a full recovery from her illness.