Anja is a 35-year-old self-taught scholar of poisons and antidotes living in the city of Four Saints. Driven by a childhood family tragedy, she relies on a rigorous, empirical approach to medicine, actively questioning established classical texts. She is socially awkward and prefers practical clothing over courtly gowns, approaching her new royal assignment with intellectual curiosity and professional detachment.

Princess Snow is the 12-year-old surviving daughter of King Randolph. Though she appears pale and listless from an undiagnosed wasting illness, she possesses a sharp intelligence and a secretive, willful nature. She harbors deep grief over her family's tragedies and hides critical knowledge about the true source of her mysterious condition.

The Mirror Queen is an awakened reflection bearing the exact likeness of King Randolph's deceased wife. Confined to the cold, soundless mirror-world, she deeply resents her derivative existence and covets the warmth and vitality of the real world. She is a calculating figure who manipulates those around her to pursue her goal of establishing a permanent existence outside the glass.

Javier is a royal guard tasked with ensuring Anja's safety during her investigation at Witherleaf. He is a stoic, observant man who communicates sparsely but possesses a sharp tactical mind. His military background and quiet capability make him an essential grounding force for Anja as her investigation uncovers increasingly dangerous elements.

King Randolph is the pragmatic and weary ruler of the Kingdom of Saints, having inherited the throne from his late uncle. Burdened by recent family tragedy, he is deeply devoted to his surviving daughter, Snow. He exhibits a practical skepticism of traditional court physicians, leading him to seek out an unbiased expert to diagnose Snow's illness.

Grayling is a talking mirror-cat who resides in the reflected world. He is an acerbic and cryptic figure who dispenses information about the rules of his realm only when bribed with treats or cream. Despite his difficult demeanor, he serves as a crucial, albeit frustrating, source of exposition for Anja.

Lady Sorrel is the former mistress of King Bastian who now resides peacefully at the Witherleaf estate. She is a warm and pragmatic woman who serves as a trusted confidante to King Randolph. She maintains a distinct aversion to mirrors, keeping them covered in her rooms due to cautious habits formed during her time at court.

Nurse is the caregiver assigned to Princess Snow. She is deeply affected by the recent tragedies that have struck the royal family, particularly the death of Princess Rose. Her interactions with Anja reveal the heavy burden of guilt and responsibility she carries regarding the royal children's well-being.

Aaron is a royal guard assigned to protect Anja alongside his partner, Javier. Unlike Javier's stoic demeanor, Aaron is talkative and conventional. He represents a standard, straightforward approach to security, focusing on immediate and visible physical threats to Anja's safety.

Scand is Anja's former tutor who shaped her intellectual development during her youth. He encouraged her unconventional study of toxic plants and antidotes, instilling in her a foundational skepticism of established classical knowledge. His teachings form the bedrock of Anja's empirical approach to problem-solving.

Princess Rose is King Randolph's deceased daughter and Snow's sister. Before her untimely death, she exhibited sudden and strange cognitive changes, such as clumsiness and an inability to read, which deeply alarmed her caretakers. Her memory heavily influences the actions of those she left behind.

Isobel is Anja's sister. Deeply concerned with the family's reputation and social standing, she worries about Anja's lack of appropriate clothing for the royal court and takes it upon herself to ensure her sister is presentably dressed for her new assignment.

Rinald is the resident doctor at the Witherleaf villa. He has been treating Princess Snow's illness with traditional medical practices, confirming to Anja that the girl's sporadic symptoms have been worsening for months despite his efforts.

Eloise is a maid working at the Witherleaf estate. She goes about her daily duties unaware of the supernatural phenomena occurring around her, sometimes unwittingly stumbling into Anja and Javier's secretive investigations.

Michael is a healer at the Temple of Saint Adder in Four Saints. He defers to Anja's specialized expertise in toxicology when dealing with a severe lotus smoke overdose, showcasing her strong reputation among local medical practitioners.

General Matthias is a kind military officer traveling with the royal retinue. He helps clarify the logistics of the king's travel schedule for Anja, noting that the larger party will soon depart for Cholla Bay.

Anthony is Anja's late cousin. When they were children, he tragically died after mistaking poison hemlock for a wild carrot. The lack of a cure for his poisoning drove Anja's lifelong, rigorous study of toxicology.

King Bastian, known as Bastian the Demon, is King Randolph's late uncle and predecessor. His reign was marked by intense paranoia, and memories of his rule continue to cast an uneasy shadow over the kingdom's politics and his former acquaintances.

Mirror Sorrel is the awakened reflection of Lady Sorrel. Unlike other entities within the mirror-world, she quietly resists the Mirror Queen's violent demands, demonstrating the same strong ethical core and intelligence as her real-world counterpart.

Jonas is a young boy in Four Saints who desperately seeks Anja's help when his brother suffers a severe overdose of lotus smoke, highlighting Anja's connection to the common people of the city.