What is the main conflict in Aura by Carlos Fuentes?

Felipe Montero stumbles upon an advertisement for a high-paying job for a French-speaking historian. He fits the description perfectly and goes to the address listed the next day. After knocking on the door and receiving no response, he walks in. The interior is completely dark but a woman's voice rings out, asking him to come upstairs. Senora Consuelo, the woman who posted the advertisement, is eager to offer him the job. She wants someone to complete her dead husband's memoirs. Without saying why, the job requires that he stay in the house. After he has accepted the job, he meets Aura, Consuelo's young, beautiful niece, and is struck by her gorgeous green eyes