The father of Safie had been the cause of their ruin.

In Chapter 14, the monster explains how the De Lacey family came to be living in poverty in a remote cottage. Only a few months before he first saw them, they lived in France, where they were wealthy, respected, and surrounded by friends. Then the son, Felix, witnessed the trial of Safie’s father, a wealthy Turkish merchant who had been unjustly sentenced to death. Horrified by this injustice, he helped Safie’s father escape, and during this time, he and Safie fell deeply in love. But Safie’s father betrayed Felix’s trust after his escape. He broke his promise to allow Felix to marry Safie and fled with her to another country. When Felix's role in the escape was discovered, his family was arrested, stripped of their property, and exiled from France.

There are multiple lessons that the monster might have taken away from the De Laceys’ sad story, including that is that not only are individuals such as Safie’s father capable of treachery, but the core institutions of human society such as its courts are deeply corrupt. Moreover, he might surmise that fundamentally decent people such as the De Laceys can quickly come to ruin in the wretched society that humans have created.