Sandro is an orphan living in Giglia. He is an apprentice spy for Enrico Poggi, the spymaster of the Duke of Giglia, and becomes the guide of Brother Tino, a new novice friar at Saint-Mary-among-the-Vines. He eventually becomes a novice friar at Saint-Mary-among-the-Vines.
Though Sandro eagerly tries to emulate his master, he grows attached to Brother Tino and his friends and becomes increasingly reluctant to divulge information that he learns regarding Tino and the Stravaganti. The boy also becomes closer to Brother Sulien, who becomes a father figure to Sandro, and the other friars at Saint-Mary-among-the-Vines. His attachment to both Tino and Sulien becomes evident when another novice friar, Brother Benvenuto, appears and Sandro becomes jealous. As a gesture of trust, Sulien reveals the existence of the Brotherhood of the Stravaganti and that he, Brother Tino, and Brother Benvenuto are members the order. Sandro agrees keep the secret rather than reveal it to Enrico and enjoys learning how to read from Brother Sulien.
When Sandro witnesses Carlo di Chimici murder Davide Nucci, he begins avoiding Enrico and winds up adopting a mongrel dog he names "Fratello". During his spare time, Sandro stays at Saint-Mary-among-the-Vines, eating and staying the company of the friars. After the massacre at the Church of Annunciation, Sandro braves the floods to retrieve a precious medicine from Sulien's flooded cell at Saint-Mary-among-the-Vines, nearly drowning in the process. Realizing that Sandro was unwilling to return to the life of a spy under his direction, Enrico releases him from his service. Sandro happily becomes an novice friar at Saint-Mary-among-the-Vines with Fratello, who is renamed Brother Dog.
He and Brother Dog adjust to their life at the friary well and enjoying the kitchens, though he often wonders what became of Tino and Benvenuto after they returned to their world and misses them. When Sulien reveals that a new Stravagante from Tino's world, a girl who will not be Georgia, will be visiting them, he eagerly waits with Brother Dog in Sulien's cell for her arrival. However, they are all surprised and Sandro is especially delighted when Brothers Tino and Benvenuto both appear along with the new Stravagante. He is quickly sent to retrieve Gaetano di Chimici and leaves Brother Dog with Gaetano and Benvenuto before going about his own business. During City of Swords, Sandro is invited as a guest to the wedding of Arianna Rossi and Luciano Crinamorte, where he is seated next to Giuditta Miele and assists Sulien during the ceremony.