Dr. Kristof Larsen, is the protagonist of the 20th-century narrative, a dynamic and round character whose journey charts a course from intellectual detachment to active moral engagement. A Dutch psychiatrist working in Paris, his profession places him in the role of an observer. Haunted by his failure to save his sister, Annelies, from suicide, he adopts a compassionate approach to medicine and opposes the cold, mechanistic methods of his superior, Dr. Claudel. Initially, Kristof manages the encroaching war through avoidance, what he calls “ostrich thinking” (33), seeking refuge in the abstract intellectualism of his work and the escapism of the Paris souterrain. His friendship with the Brodsky family, however, provides him with a personal connection and incentive, transforming the abstract threat of Nazism into a direct danger to people he loves. In this respect, Kristof’s character is an interpreter-guide for the reader of the many disturbing and alien elements of the Nazi occupation of Paris.

As a result, Kristof’s transformation from a passive witness to a committed member of the French Resistance models the novel’s message of empathy and shared humanity. The implementation of Aktion T4 at Sainte-Anne’s, a program of systematic murder disguised as medical protocol, forces him to confront the reality that his profession has been co-opted as an instrument of oppression. His decision to falsify patient records is a key act of defiance, marking his transition from a man of science who follows rules to a man of conscience who breaks them to save lives. He recognizes that in the face of such deep evil, neutrality is a form of complicity. This moral reckoning is central to his character arc, as he learns that true healing sometimes requires subversion rather than treatment.

Kristof’s role evolves further after the arrest of the Brodsky family, when he becomes the protector of their daughter, Sasha, and three other Jewish teenagers. This responsibility pushes him beyond the confines of the hospital and into the dangerous world of escape networks, fully embracing the purpose of the souterrain as a pathway to freedom. Guided by Alesander and Ursula, he learns to navigate a world of clandestine operations, where trust is a carefully vetted commodity and survival depends on courage and ingenuity.

Sasha Brodsky is a dynamic and round deuteragonist whose coming-of-age story is violently accelerated by the trauma of the Nazi occupation. At 12, she is a precocious and intellectual girl, more interested in classics and her mnemonic project of memorizing Ovid’s Metamorphoses than the world’s encroaching darkness. Her “memory palace” is initially an academic exercise, but as the occupation strips away her freedoms, her home, and her family, it becomes an essential internal sanctuary. This project links to theme of art and culture as means to preserve memory and identity, as she uses the ancient myths of transformation to process her own losses. 

Sasha’s resilience is her defining trait. As antisemitic discrimination and oppression escalate in Nazi-occupied Paris, she experiences the ostracism of friends and the chilling indifference of teachers, retreating into an inner world marked by defiance. Following her family’s arrest, she becomes a fugitive. Her journey into the souterrain with Kristof is a literal and symbolic descent into the underworld, where she must rely on her intelligence and inner strength to navigate the physical darkness and her grief. In the tunnels, she transitions from a protected child into a resourceful and essential member of the underground community, using her knowledge of myth and memory to inspire hope and document their journey.

Sasha’s relationships with the other teenagers, particularly Gérard, illustrate the formation of a chosen family through shared trauma. Her connection with Gérard offers a source of hope and humanity amidst the chaos. By the end of her journey through the tunnels, Sasha has transformed from a girl who loves stories to one who understands that stories can be a form of survival. This is encapsulated when she marks Alesander’s impromptu grave with a line from Horace and a liberty bird, demonstrating her role as one who creates meaning and guidance for those who will follow.

Étienne Duchamp is the deuteragonist and Alouette’s romantic interest in the 17th-century timeline. A stoic and responsible quarrier, he is defined by his connection to the limestone that forms the foundation of Paris. His work underground is a legacy passed down through generations, but it is also a seemingly inescapable fate that promises an early death. Initially resigned to this life, Étienne is practical and grounded, his primary motivation being the care of his grandmother and his orphaned niece and nephew. His life is one of hard labor and quiet endurance, in contrast to Alouette’s fiery, intellectual ambition.

Étienne’s relationship with Alouette drives his character’s transformation, awakening a desire for a life beyond survival. He is drawn to her intelligence and her defiant spirit, recognizing her will to shape her own destiny. This inspiration leads to his own acts of quiet rebellion. Learning to read and write is a significant step toward self-determination. His central act of creation is the carving of stone larks for Alouette: This is the novel’s primary symbol, connoting love, hope, and self-expression. 

Étienne’s journey is internal and practical. He moves from accepting his predetermined path to actively seeking a different future. His decision to abandon the profitable but dangerous smuggling work in the quarry is an important moral turning point. By the novel’s end, he has fully committed to a life with Alouette, choosing to follow her into an uncertain future. He evolves from being defined by his circumstances to defined by his choices and sense of agency.

Alesander Extebarria is a charismatic and enigmatic deuteragonist, a mentor figure to Kristof in the 20th-century timeline. Initially introduced as a carefree Basque architecture student with a passion for exploring the Paris souterrain, he is later revealed to be a deeply committed and experienced member of the French Resistance. His understanding of architecture gives him a unique ability to see and utilize the city’s structural vulnerabilities for the resistance cause. This dual identity is central to his character’s role, which embodies the theme of The Physical and Conceptual “Underground” as a Space for Resistance. Alesander’s character is a key force in Kristof’s narrative arc from passive sympathy to action, forcing him to confront the reality of the Aktion T4 program. 

Alesander’s motivations are rooted in personal loss and political conviction, stemming from his experiences fighting Franco in the Spanish Civil War and the arrest of his first resistance cell in Paris. These traumas have forged him into a man who can be pragmatic and ruthless but who is driven by humanistic principles. Despite his hardened exterior, Alesander retains a sense of playfulness and a deep appreciation for art and history, seen in his game of Exquisite Corpse and his stories of the souterrain’s past. His death is a key narrative moment, a sacrifice that solidifies the group’s resolve and transforms their journey from an escape into a mission. Through his maps and his example, he leaves a legacy of courage and “a clear path” (409) for the others to follow to safety.

Henriette Voland is a key minor character who shapes Alouette, her daughter. Initially remembered as a woman broken by the grief of multiple stillbirths and suffering from recurrent psychological crises, Henriette is a cautionary tale in the novel for what happens to women who cannot escape the oppressive environment of Saint-Marcel. In this, she is a foil to Alouette, and a driver for Alouette’s desire for escape. Initially, Henriette’s absence from the family has created a deep scar of resentment in Alouette, and a fear of repeating what she sees as her mother’s mistakes. When Henriette returns, however, she is complex and resilient woman, unlike the fragile figure of Alouette’s memory: Her warnings about the guild’s dangers are revealed as the prescient and astute observations of a survivor. Her story of finding sanctuary with the Sisters of Saint Catherine offers an important matriarchal model that Alouette will later follow, structurally resolving their past conflict. Henriette’s parting words to Alouette, “The dye is not set” (164), encapsulate the novel’s message of self-determination against a seemingly fixed fate.

Felix and Rachel Brodsky are round, static supporting characters who represent the human heart of the 1940s narrative. The novel uses the Brodskys to dramatize and personalize the historical events of the Holocaust from the perspective of its victims. Polish Jewish refugees, they have built a family life in Paris filled with warmth, intellect, and resilience. Felix, a skilled watchmaker, is patient and philosophical, his love for the game of Go symbolizing a strategic and hopeful approach to life’s challenges. Rachel is pragmatic and fiercely protective, her resourcefulness turning meager rations into loving meals and her home into a sanctuary. Together, they provide their neighbor, Kristof, with a found family, grounding his anxieties about the war in a tangible, loving relationship. Their apartment is a haven of normalcy and culture in a city succumbing to fear. Their sudden arrest and separation are the central tragedies that galvanize Kristof and sets the second half of the plot into motion, transforming the political into the deeply personal.