This series of three novellas is unified by an overarching motif: in all three tales, a mysterious secret society known as The Thirteen is at work behind the scenes. The men in the group have pledged eternal loyalty to each other, and if any member ever finds himself in peril, it is the sworn duty of the others to come to his aid. Honore de Balzac uses this premise as a device to explore a wide range of topics, including clashes between different classes of society, doomed romances, and intrigue driven by greed.