Serilla became a Heart Companion of Cosgo's father, the previous Satrap of Jamaillia. When Cosgo inherited the throne, he began treating his Companions more like a harem than a panel of advisors. Serilla strongly dislikes Cosgo and refuses his advances.
Serilla is concerned about unrest in Bingtown, as Cosgo refused to acknowledge a contingent of Traders that recently sought audience with him. She attempts to persuade him to give her permission to act with his authority in Bingtown, believing that she is far more capable of maintaining control there. Instead, Cosgo announces that he will undertake a voyage there himself.
Serilla's tolerance of Cosgo's rudeness and hedonistic behavior wanes during their long sea voyage up the coast, and she eventually defies him. Cosgo threatens her with violence, but she stands her ground, believing that he is bluffing. Cosgo gives her to their Chalcedean captain, and Serilla is confined, beaten, and subjected to repeated rape for much of the rest of their voyage.
She is eventually freed when Cosgo falls ill and asks for her care. Newly determined to seize her own power, Serilla does all she can to maintain an image of nursing Cosgo back to health, demanding regular baths and plentiful food and drink. She indulges in most of these things herself while keeping Cosgo in a state of weakness via a regiment of emetics and flavorless food. During this time, she persuades Cosgo to finally grant her the full authority of the Satrapy in all matters concerning Bingtown. She allows him to gain some strength shortly before their arrival in Bingtown.