Whitford Hayes, whose nickname is Whit, is Inez’s love interest and the other first-person narrator of Where the Library Hides. A rough-edged former soldier, Whit currently works as Ricardo’s aide-de-camp. He was dishonorably discharged from the military after attempting to help General Gordon when commanded otherwise and developed an alcohol addiction while trying to cope with physical and emotional scars. His experiences hardened him, making him wary of trusting others. However, despite his gruff demeanor, Whit is deeply protective, particularly of Inez, whom he grows to love fiercely. While their romance is tumultuous and built on the enemies-to-lovers trope, he refuses to abandon her and takes a bullet for her during the fight with Isadora in the ruined lighthouse.

Navigating the Complex Bonds of Family thematically motivates Whit, just like Inez. He’s the younger son of a British aristocratic family in deep debt as a result of his father’s gambling habit. Whit’s defining characteristic is his loyalty. When he betrays Inez, it’s only to save his beloved sister, Arabella, who’s being forced to marry an older, wealthy man to solve their family’s financial issues. Whit cares about Inez but prioritizes his sister and his family’s well-being more in the beginning, telling Inez, “I can’t apologize for saving my sister, because I would make the same decision all over again” (128). Nevertheless, he does attempt to rectify the situation, albeit secretly. For most of the novel, Whit focuses on obtaining the Chrysopoeia of Cleopatra. Originally, his objective is to create wealth to save his family from debt, but eventually, it’s to repay Inez for what he stole from her. It represents a dream of redemption and a future in which he and Inez can be together. He tells her, “I need it to make everything right between us” (347). While she insists that the money doesn’t matter to her, he still experiments with and succeeds in replicating the experiments that the scroll describes. In the end, he becomes more open with Inez, is physically selfless with her, and makes up for what he stole at the beginning of the novel.

A major supporting character in the novel, Inez’s half-sister Isadora Fincastle is the product of Lourdes’s affair with Mr. Fincastle, the head of security in Ricardo’s excavation team. She’s the epitome of grace and propriety, the opposite of Inez. She has delicate features, polished manners, and an elegance that makes her seem like she was plucked straight from high society. When she arrives at Shepheard’s Hotel and reveals her blood relationship with Inez, she seems to offer companionship at a time when Inez feels abandoned and betrayed. She presents herself as warm, curious, and, above all, supportive of Inez. This positions her as a foil for Whit, whom Inez distrusts at this point.

As the story progresses, subtle changes in Isadora’s character hint at her true nature as one of the novel’s main antagonists. While she initially maintains a soft, composed presence, moments of frustration or stress cause her carefully cultivated mask to slip. Whit is among the first to notice something amiss and continually alerts Inez to Isadora’s deceptions, including when he accuses her of warning their mother away from the bank in Alexandria.

The revelatory moment comes when they reach the ruins of the ancient lighthouse, and Inez has a vision of the location of the Chrysopoeia of Cleopatra. When Isadora turns her gun on Inez and Whit, her physicality changes to reflect the complete abandonment of her ruse: “It wasn’t just her expression that had changed. No, she seemed like an entirely different person. Her movements were less polished, less perfect, all traces of the lady she had been gone” (271). Every ounce of polish, aristocratic control, and cultivated charm disappears.

Unlike Inez, who grew up yearning for her mother’s love from afar, Isadora was raised in Lourdes’ world. Nevertheless, Isadora constantly desired approval, shaping herself into someone willing to do anything to maintain her position. Her resentment toward Inez stems from her mother’s affection for Inez. Isadora’s identity relies on her perceived position in Lourdes’ life, and Inez’s very existence threatens that.

In the end, it isn’t Inez who defeats her but Isadora herself. Her obsession with besting her sister to prove her superiority leads her to take one step too far. Despite all her manipulations, her actions leave her powerless, a tragic figure whose jealousy leads to her demise.

Inez’s missing father, Cayo Olivera, is a major antagonist in Where the Library Hides and is revealed to be the mastermind behind everything. For most of this novel and the previous one in the duology, he appears under the pseudonym of Basil Sterling, an officer in the Antiquities Service and the founder of the smuggling ring Trader’s Gate.

Cayo is a man of duologies. The novel introduces him through Inez’s memories of him as a soft-spoken scholar whom she looked up to all her life. For much of the book, she believes he’s dead and mourns him. However, he interacts with Inez as his alter ego through a combination of a magic-touched fake mustache that alters his appearance and a difference in the way he carries himself. As Sterling, he exudes confidence, ruthlessness, and control. He demands obedience and punishes betrayal with death. Inez struggles to reconcile these two versions of him, especially with the morals she knew her father to have. Cayo justifies his actions by claiming that his original intent was to stop the illegal flow of artifacts out of Egypt but that, over time, he succumbed to the very corruption he sought to fight. He admits to Inez, “I was down a road I never thought I’d travel, and one day I realized that I couldn’t turn back” (322). The corruption he once tried to end has now entirely consumed his life. The artifacts he sought to protect became commodities, and the moral boundaries he once respected became obstacles. Inez’s involvement in the plot is purely due to his orchestrations. He sent Cleopatra’s ring to her in the first place, only to steal it back as Sterling. Everything he did was to test Inez to see if she was worthy of inheriting his criminal empire or, as his daughter puts it, “to see if [she] was corruptible” (328).

As revealed in the first novel, Cayo is dying of consumption and believes that Cleopatra’s mummy is the only cure for his condition. He becomes obsessed with finding her and with punishing Lourdes for her betrayal. His physical deterioration mirrors the decay of his moral compass, and despite his intelligence and ruthlessness, Cayo’s downfall is inevitable. As the library collapses around him, he remains fixated on his prize, unwilling to abandon his pursuit even as death claims him.