The chapters detail the harsh new reality of Lisette, a former noble stripped of her status and wealth, as she is exiled to a dungeon domain. Her half-sister, the Saint Merdiana, orchestrates this punishment, fueled by jealousy and a desire to usurp Lisette's position and inheritance. Lisette, despite her dire circumstances, maintains her pride and knowledge, entering the fortified town of Norn, which has grown around a dungeon. She is given a sinner's identification card, detailing her immense debt of 50 million gold to the church, the only path to purification.
Upon entering the dungeon, Lisette encounters Rannial Madore, an alchemist elf who, despite her initial skepticism about Lisette's unpreparedness, gifts her a "Substitute Heart" amulet, allowing a single resurrection, and an item bag. Lisette, possessing the "Noble Bloodline" skill which grants triple skill points, strategically acquires "Preemptive Action" and "Fire Magic (Beginner)." She enters the dungeon, a vast, seemingly natural forest, and immediately faces slime monsters. Using her "Preemptive Action" and "Flame Arrow," she defeats them, realizing her potential. She also discovers that monsters are edible and, driven by hunger, cooks and eats a frog. Her combat prowess is further tested against a "Giant Flying Urchin," which she defeats with a powerful "Flame Lance," obtaining a valuable amber stone.
Lisette then visits the Adventurer's Guild, where she is registered and her rapid dungeon progression is noted with astonishment. Despite rumors about her, she declines offers to join parties, preferring to adventure alone. She is saved from a predatory adventurer by Leonhardt, the leader of a promising party. Lisette begins taking simple quests, earning gold by selling monster materials. She then visits Rannial's shop, "Black Cat's Alchemy Pot," to purchase supplies for extended dungeon living, including cooking equipment and potions, as she intends to avoid the surface world due to the rumors and potential pursuit.
Meanwhile, Merdiana, on her return journey, revels in Lisette's supposed downfall, viewing it as deserved punishment. She manipulates a church knight into actively seeking Lisette's demise. Merdiana's own insecurity stems from her illegitimate birth and her belief that Lisette unjustly received the Saint's mark. At a church, Merdiana attempts to use her Saintly powers but fails, attributing it to the locals' lack of faith.
Lisette, now living in the dungeon, adapts to its unique environment, noting the absence of day and night. She discovers that monster meat has restorative properties and begins to enjoy her dungeon life, finding freedom there. She acquires new skills: "Appraisal," "Purification Magic," and "Barrier Magic," enhancing her survival capabilities. She also gains "Water Magic (Beginner)," allowing her to freeze water.
Her exploration leads her to a second layer of the dungeon, a water-filled, stone-like area resembling an underground waterway. She encounters dangerous water-dwelling monsters like "Water Reapers" and "Merfolk," defeating them with her magic. She discovers a hidden area with a locked door, which she opens using her magic. Inside, she finds a dying Leonhardt, whom she rescues and nurses back to health, preparing him a nourishing soup made from unicorn meat and dungeon-grown ingredients.
