Doctor Pascal practiced medicine for twelve years. He now lives off his investments and has devoted his life to research on heredity. He has a giant armoire filled with his findings, including files on each of his family members. His mother, Madame Rougon, worries about her son. She had expected him to become a famous doctor. Instead, he accumulates possibly scandalous files about his family.

Madama Rougon tries to enlist Clotilde, Doctor Pascal’s niece, into her cause. Clotilde lives with her uncle and is loyal to him, but she sometimes fears that her uncle is tampering with God’s plans. One day, Clotilde gives in to Madame Rougon’s pleadings and gives her the key to the armoire. Dr. Pascal surprises them rifling through his work. He feels as if his family has betrayed him.

Clotilde repents, but when a Capuchin preacher comes to town, she again changes her mind and tries once more to destroy the files. Pascal once again catches her and to regain her trust tells her all about his project. She is half-convinced and promises to think it over.

She is also considering a marriage proposal from Dr. Ramond, whom she consults when Pascal falls ill. Pascal is afraid he is going mad, but he recovers, having received a serum Ramond invented. At this point, Pascal realizes he is in love with Clotilde, but so as not to interfere in her young life, he presses her to marry Ramond. She admits she can’t for she loves Pascal.

They become lovers, but Clotilde is called away to her ill brother in Paris. She returns home when she discovers that she is pregnant, but Pascal dies two hours before her arrival. Before his death, he had completed his files, but M. Rougon and his old servant Martine burn them.