Franco is a senior apprentice to the sculptor, Giuditta Miele. Described as having the face of an angel and being very charming, he becomes devoted to Giuditta, who proves to the one the few people who are not at all taken in by his charm. He has silvery-blond hair and pale skin, unusual traits that he inherited from his mother from northern Europa.
Because of his good looks, Franco often takes jobs modeling as an angel for other artists in Giglia. He is somewhat bold and appears carefree in his actions, taking the lead after suggesting that looking at sketches of the young Duchessa of Bellezza's unmasked face is fine and then commenting that her maid was more attractive. He is popular with attractive women, often spending his nights out in their company, and giving lascivious looks to girls he finds attractive.
Franco spends most of his days working in the bottega of Giuditta Miele. She trusts him implicitly and he loyally gives her information that he has gleaned while working for other artists; through Franco's session with painter Bruno Vecchietto, Giuditta learns that the Nucci are stockpiling their armoury for a conflict with the di Chimici. Towards the end of the novel, Franco is a key figure for enabling Luciano Crinamorte's escape from Giglia when Fabrizio di Chimici orders Luciano's arrest. Franco drives the cart containing the crate with the marble sculpture of the Duchessa of Bellezza created by Giuditta as a commission from the Duchessa. Unbeknowst to the guards around the city looking for Luciano, the young cavaliere has been hidden inside the crate. Franco, holding his temper in check when the guards make lewd remarks about Giuditta, persuades the guards not to open the crate and successfully smuggles Luciano out the city to take him and the statue to Bellezza.
Franco makes a brief appearance in City of Swords, after Mortimer Goldsmith accidentally stravagates to Giuditta's bottega using a sketch of Georgia O'Grady that Giuditta made as a talisman for Alice Greaves. After Giuditta scolds him for taking Mortimer's sketch, Franco respectfully returns the drawing and apologizes, asking whether Mortimer is Georgia's grandfather.