Man and Wife (1923)

Dora Perkins is a country girl who runs away to New York City. She gets work as a nurse and marries Dr. Howard Fleming, a famed brain surgeon. Supposedly she dies in a fire, and some time later Fleming takes a vacation in the country, where by some odd coincidence he winds up meeting Dolly, Dora's sister. Without realizing her relationship to Dora, he marries her. Soon Dolly is expecting, and not long after, Dora pops up -- she survived the fire, but has been left hopelessly insane.