General Ferrucci, an exiled enemy of the Duke de Medici, accepts an amnesty from the Florence tyrant and returns to the city. Marco is outraged because his old mentor has apparently turned his back on the Republican cause.
When a butcher refuses to pay a tax, de Medici orders Rodrigo to kill him. The officer plots to have Marco do the deed for him by starting a rumor that the portrait painter has taken liberties with the butcher's beautiful young wife, thereby causing a duel that the older man will lose.
Fearing a revolt because of his high taxes, de Medici hires Spanish mercenaries to keep the peace. The peacekeepers methods include a large amount of violence, however, and de Medici hopes that one of the victims is Marco.
A Republican courier is ambushed and his message to a man only known as "Orsini" is stolen by de Medici's agents. A man is sent to spy on Marco hoping that he will unwittingly reveal Orsini's true identity.
In order to impress a visiting nobleman, the Duke de Medici commissions elaborate decorations and then refuses to pay for them. The artisans plot to force the Duke to compensate them for their efforts.
Stephano tries to get the Duke of Urbino to invest in a ship for Far East trade, but the Duke de Medici needs to borrow money from the same man. Marco plots to help Stephano get his ship and tweak the noses of the two Dukes in the process.
Two powerful Italian families are to be united by a marriage of convenience. The principals in the wedding have never seen each other and Marco is hired to paint a portrait of the bride to be - a beautiful woman who, unfortunately has a nasty scar on her face. Marco can't decide whether to include the disfiguring mark in his portrait.
In order to raise money to buy expensive brass cannon, De Medici connives with the Artists' Guild leadership to ban the possession of classical and pagan art, then plans to sell the confiscated works to an Milanese art dealer.
When Leonardo da Vinci visits Florence, the Duke De Medici attempts to purchase his plan for a submarine. When Leonardo refuses, De Medici orders his men to search his rooms and those of his friend, Marco del Monte.
After a ten-year voyage full of perils, a famous sea captain returns to his family in Florence. He is not aware of the dalliance between his wife and Captain Rodrigo, nor that his wife has entrusted his fortune to De Medici's care. Meanwhile the Duke is taking steps to eliminate the Captain and everyone who has come into contact with him since his arrival.
Marco and Angelica convince the British ambassador to disguise himself as a guildsman to learn about De Medici and his evil policies before loaning him the money that the Florence despot has requested. De Medici learns of the plot and orders his henchman to murder the diplomat before he presents his credentials.
De Medici plans to charge a high tariff on a shipment of alum being delivered to Florence to keep his prices for the key ingredient for paint and make-up extremely high. When Marco's scheme to smuggle the alum over the walls is thwarted, Angelica organizes the women of Florence to protest the high prices by refusing to wear makeup.
After Marco and Sandro rescue a woman from a pair of would-be kidnappers, the artist discovers the damsel in distress is Cristina, his former fiancée who left Siena rather than elope with him. Later that evening Marco has a visit from a Republican leader who is trying to reach Rome and wishes him to guard his sister from the thugs who are trying to capture her. That woman is the lovely Cristina.
Over Machiavelli's objections, De Medici insists on negotiating an alliance with France. Meanwhile, the French ambassador convinces the love-struck Francesca into joining a plot to overthrow her brother.
De Medici commissions Marco to paint a portrait of his beautiful sister, Francesca, wearing the priceless necklace she will inherit on her 18th birthday. When Marco insists on making the painting in his studio, De Medici sees an opportunity to steal the necklace and blame the artist for the crime.
Before the mortally wounded prime minister dies, he asks an elderly puppet-master to deliver a message to Marco to warn the Duke of Padua of an assassination plot. Before the old man can find the artist, he's arrested by De Medici's agents. Marco must find a way to learn the contents of the message before the Duke leaves Florence.
The republicans are three days from attempting to overthrow the Medicis, but are concerned that one of their noble supporters might be secretly planning to provide troops for the Florence's dictator. A female courier with important information about troop dispositions arrives, but is too frightened to remember the message she was to convey to Marco and his friends.
Marco is falsely accused of murdering Count Origi by his ward who will inherit the nobleman's fortune. The count wrote the name of his real attacker on a letter listing the names of republican leaders, so Marco cannot introduce the document in his defense without betraying his friends.
Angry about his young sister's extravagance and scheming, De Medici arranges for a widow from an influential Roman family to become Francesca's female companion. Soon after she arrives, a series of unusual events cause the Duke to question his young sibling's sanity.
Otello, an itinerant swordsman, comes to Marco's rescue when he beset by three attackers. In gratitude, Marco allows the visitor to stay in his rooms. Later, Otello goes to meet the man who invited him to Florence - the Duke De Medici, who wants to hire him to assassinate Marco.