Alessandro Manzoni reached back two centuries to set The Betrothed within the complex history of Italy before national unification. The powerful nobles of the different regions brutally exercised control over the peasants in their territories and sustained complex alliances and feuds with the leaders of other duchies and kingdoms. By focusing on the plight of two lovers who endure all manner of hardships before they are finally allowed to marry, the author emphasizes the human cost of the social turmoil of the times. He also exposes the corruption within the Catholic Church that went hand in hand with the political intrigue.

While Lorenzo and Lucia truly love each other and are ready to marry, the evil Don Rodrigo thwarts their plans because of his own lust for the young woman. Not only are the lovers sent away for their own safety before Rodrigo's men can abduct her, but they must find refuge in separate locations. Lucia and her mother enter a convent, where they are temporarily safe.

Lorenzo, on the other hand, travels alone and gets caught up in a bread riot and ends up in jail. His youthful foolishness has serious consequences, as he must flee Milan. Unfortunately, this means that Lucia is now unable to find him. However, he gets work in silk manufacturing—an important commercial enterprise of the time; in this transition, he is representative of the transition of the peasantry into artisans and the development of a new class hierarchy that was a significant change in this period.

The theme of pestilence or plague enters the novel as both lovers, like thousands of other Italians, succumb to the disease—at least for a while. While Manzoni stresses the literal contagion and its devastating effects, he also suggests that the figurative significance of social evils' effects are paralleled by the physical sufferings.

The alliances that were forged between the nobles do not hold up, as the Un-named noble that Rodrigo thought would back him decides not to follow through. The idea that a pure young beauty could move such a powerful man seems a sign of hope for the nation's future; Manzoni suggests that some members of the aristocracy exhibited good morals and behavior.

In the convent, Lucia soon learns that corruption has tainted the nuns. Her chief ally, caught in a murderous plot, turns on her, forcing her to move to a new location. In the second convent, Lucia finds the faith that had eluded her and decides to become a nun. Lucia eventually decides against committing to be a bride of Christ, however; she realizes that a secular—though still devoted—life is her desire. The proper union of the lovers at the novel's end can also be seen to foreshadow the larger social unity that Manzoni envisioned for his land.