Hatty Moulton (née Doran) was an American heiress, the only daughter of Aloysius Doran from San Francisco.
In America, Moulton secretly married Francis Hay Moulton without her father's knowledge, because the older man disapproved of the match due to Frank's lack of fortune. Frank then left his wife after the wedding to search for his own fortune, so he could return to her as a rich man. Later he was reported killed. Hatty later got engaged to a British nobleman, Lord Robert St Simon, the second son of the Duke of Balmoral.
Believing Frank to be dead, she intended to become a good wife to Lord St Simon, despite still loving her husband, but on the planned wedding day, she saw to her astonishment Frank was alive. He managed to pass on a message to her asking her to meet with him as soon as possible after the ceremony. They decided to run away together, because Hatty was ashamed of having cause so much trouble for her fiancée and her father with that secret she had. But Sherlock Holmes tracked them down and advised them to come forward with their story to great disappointment of Lord St Simon.