Marco's first appearance in the series occurs in City of Masks during the Feast of the Maddalena. He is the burly mandolier of Silvia Bellini's private mandola during the festival, unaware that he is sculling the Duchessa's boat because Silvia elected to use a body double for the Duchessa's public appearance. When the assassination attempt on Silvia is foiled by Lucien Mulholland, Silvia orders Marco to discreetly row the mandola back to the Ducal Palazzo as quickly as possible to thwart Rinaldo di Chimici's plans. Marco is later rewarded with a post as a footman at the palace for his services.
Marco does not appear directly in City of Flowers, but is implied to be the burly footman scolded by Barbara before Arianna departs for Giglia. Barbara later reveals that she is engaged to be married to him and that they both intend to remain in Arianna's service after they marry.
Marco becomes Arianna's bodyguard at Barbara's insistence in City of Secrets when Arianna begins anonymously visiting Luciano in Padavia. With the support of the Regent and his wife, Marco is trained by Guido Parola and suitably armed with a Merlino-fish dagger to protect the Duchessa. He aids his mistress's efforts to save the Manoush from persecution in Padavia, and they all later attend his and Barbara's wedding at the conclusion of the novel.
He continues to act as the Duchessa's personal bodyguard in her anonymous visits in City of Ships. Though he does not know of the Stravaganti, he recognizes Nick Duke and Georgia O'Grady are allies of the Duchessa when he notices that they lack shadows and safely delivers them Arianna when the duo suddenly appear in Bellezza. By the events of City of Swords, Marco is well-regarded as the Duchessa's favourite footman and she permits him to be one of the mandoliers sculling her mandola during the Marriage with the Sea.