Shortly after Harriet's death, Shelley and Mary married, now with Godwin's blessing. Their attempts to gain custody of Shelley's two children by Harriet failed. Even though this happened, their writing careers enjoyed more success. In the spring of 1817, Mary finished "Frankenstein". Mary had two sons and a daughter. The daughter died in infancy and the elder son when he was two. Mary and Percy were both vegetarians, and strong advocates for animal rights. One can see references to vegetarianism in her writing. For example, in her novel "Frankenstein", the 'monster' was a vegetarian. After Percy's death in 1822, she returned to England to finish Shelley's writings and educate their only surviving child.