By the end of the eighteenth century, there was a growing sense of disruption caused by the Industrial Revolution and the French Revolution. The Industrial Revolution brought the liberating power of technology, but such rapid expansion also brought pollution and the spoiling of the natural world. Human beings were being uprooted, and certain types of traditional work had been lost. With the redistribution of wealth and poverty under a capitalist system, labour management became more impersonal. The French Revolution brought social, political, and ideological change along with disillusionment through terror and the rise of Napoleon.

Percy Bysshe Shelley was still at Eton in 1810 when "Zastrozzi" was published. He would have appreciated the Gothic's ability to create dramatic and psychological tension along with real evil, even if it was disguised as virtue. A villain can have a single weakness, but to describe a person as totally evil is to deprive them of the choice to which they may fall victim. The more the character reveals about their past and the choices they have made, the more the reader recognizes that they once had the power to reject evil motives and embrace benevolent ones. In "Zastrozzi," the characters' liberty or freedom of choice is often physically or psychologically restricted, either by the schemes of others or by some overwhelming passion.

Tillotama Rajan, in his analysis of the early works of Shelley, refers to "Zastrozzi" as a pastiche that does not refer to the real world but to other texts, literary, social, and moral. It borrows both names and plot points from other Gothic novels. Foucault sees this as a new form of literature developing in the 19th century, where texts are "linked to the vast world of print" and develop "within the recognizable institutions of writing." This opens up a space wholly dependent on the network of books formed in the past. Along with being a patchwork of ideas, the novel has been described as melodramatic, as there is no interiority to the characters, and they appear flat.

The novel begins with a quote from Milton's "Paradise Lost," suggesting the creator destroys his creation as a work of more than common revenge. This sets the destructive tone for a novel of cruelty and vengeance. It speaks of secret enemies, revenge, a dark night, and vengeance; however, it is not until much later that we learn Zastrozzi's motive for revenge. Verezzi's father had seduced Zastrozzi's mother, and after she became pregnant, he abandoned her. Upon her death, Zastrozzi swore revenge on both the father and son.

Verezzi is in love with the idealized Julia, but Matilda, Countess di Laurentini, is also in love with him and plans to have Zastrozzi murder Julia to enable her to win Verezzi. Julia mirrors Lilla from Charlotte Dacre's "Zofloya," a pure, innocent, unattainable image of womanhood. The name Matilda is taken from Matthew Lewis's "The Monk," but unlike his character, she is no demonic force, as Shelley's focus is very atheistic.

Instead, she has the dark countenance and desire of Dacre's Victoria. Like Victoria, Matilda is the dark counterpart to Julia's light innocence. In his pursuit of Julia, his idealized soulmate, Verezzi is neither physically nor psychologically strong, and when he believes she is dead, he falls into a fever. Matilda takes him to her home, Castella di Laurentini, outside of Venice. Dark castles were often used in the Gothic to imprison their victims, and Dacre also uses a castle outside Venice as the scene for murder. Matilda's intention, much like Victoria's, is to win over the hero with her charm. Like Lewis's Matilda, she plays the harp, and momentarily, Verezzi is enraptured by her playing, but his thoughts always turn back to Julia.

Zastrozzi suggests a plan to break Julia's hold over Verezzi. Disguised as a ruffian, Zastrozzi will attack Verezzi, and when Matilda gets hurt defending him, he will see her in a different light. Again, when Victoria defends Berenza, he is so grateful that he asks her to marry him. The fact that Verezzi transfers his affections from Julia to Matilda so quickly suggests he is in love with the image more than the person. They are married and about to leave when Matilda is summoned by the Inquisition. When Julia comes to Matilda's house, Verezzi is struck with remorse and stabs himself. Like Dacre's Henriquez, he feels he has been deceived and can no longer live with the guilt. Matilda picks up the dagger and stabs Julia in a frenzied attack, reminiscent of Dacre's Victoria and Lilla. Both Matilda and Zastrozzi are brought before the Inquisition, where Matilda recants and finds religion, and Zastrozzi dies on the rack. Unlike Lewis and Dacre, Shelley removes the demonic element and resigns his characters to an earthly punishment, even if it is at the hands of the Inquisition.

Both Matilda and Zastrozzi seek individuality by transgressing the boundaries of what is acceptable to society, religion, and female propriety. Matilda is unusual for the early nineteenth century to be financially independent and therefore have no need to get married. However, propriety dictated that women did not initiate a relationship but waited for a male suitor to show a preference. Although the Romantics preferred boldness over the restraint of the eighteenth century, it is unlikely Shelley's readers would condone Matilda's aggressive actions. Zastrozzi would have been breaking biblical commandments by taking a life, along with Matilda. When he discusses it with Matilda, he rejects the immortality of the soul, and although the narrator condemns such impiety, the view cannot be erased from the reader's mind. Shelley makes mankind responsible and punishable for their own actions without divine intervention. In this sense, he is adopting a more stoic approach, which suggests destructive emotions come from errors in judgment.

The Critical Review of 1810 condemned "Zastrozzi" as gross, wanton, and unfit for the eyes of modest young women, even going so far as to say it was only fit for the eyes of a brothel. Lewis's "The Monk" was equally condemned as blasphemous when it was published, and Dacre's "Zofloya" was unfavourably and unjustly compared as a copy of "The Monk," along with being unsuitable from the pen of a lady.