Answer:
In the summer of 1816, Mary Shelley visited Geneva Lake (Switzerland) and spent her days in Switzerland with Lord Byron, Percy Shelley, and Dr. John Polidori. One day, after reading a collection of German short stories, called Fantasmagoriana, they decided to write their own short, supernatural stories.
Her story was called Frankenstein. Mary Shelley decided to convert her story into a novel, so she continued to write it until she finally completed the novel in 1817. The novel was first published anonymously, in 1818.