The story begins with Raust, a healer, being abruptly expelled from his party, "Lightning Sword," by its leader, the warrior Margulus. Margulus and the rogue, Saberria, accuse Raust of causing their failure to defeat a Hydra during a recent quest. Raust realizes this is just another instance of them scapegoating him, as their poor performance, stemming from a late night of revelry, was the true cause of the quest's failure. Even the mage, Amelia, who harbors feelings for Margulus, sides with him, directing blame towards Raust.
Raust accepts his expulsion, having endured similar mistreatment and receiving only a quarter of the party's rewards due to his perceived deficiency as a healer. He can only cast basic healing magic and struggles with advanced purification, though he has improved his skills through diligent practice, even gaining some proficiency in front-line combat and trap detection. Despite his limitations, he is grateful to Lightning Sword for including him, as other parties would not accept him. He leaves their shared residence, relinquishing his equipment.
The next day, Raust seeks to form a new party at the Adventurer's Guild, but no one responds to his recruitment notice. His reputation as a "flawed healer" precedes him, and potential allies are unwilling to associate with someone perceived as a liability. Facing financial hardship after an expensive night at an inn, Raust considers venturing into the dangerous labyrinth alone but deems it too risky. Just as he resigns himself to hunting weaker monsters in the upper levels, a beautiful, young girl named Narsena approaches him and asks to join his party.
Narsena, a skilled martial artist, expresses her desire to team up with Raust, despite his self-proclaimed flaws. Raust, initially surprised by her beauty and apparent strength, accepts her offer. Together, they venture into the labyrinth, heading towards the lower levels. Raust is impressed by Narsena's combat prowess as she effortlessly defeats Orcs, creatures known for their toughness and skill. He realizes she possesses exceptional talent, wielding two powerful skills and demonstrating remarkable combat ability. Convinced of her strength, Raust proposes they descend to the lower levels immediately, a suggestion Narsena readily accepts.
Their descent is interrupted by a sudden attack from a Worm, a creature that emerges from the labyrinth walls. Raust, demonstrating surprising agility and combat skill, swiftly dispatches the Worm with a dagger, much to Narsena's astonishment. He downplays his actions, attributing them to his "jack-of-all-trades" nature, but Narsena is clearly impressed by his unexpected prowess.
Upon reaching the lower levels, they are immediately ambushed by a formidable combination of Ogres and a Lich. Narsena expresses concern about their ability to fight such powerful foes, but Raust, confident in their combined strength, declares he will draw the enemies' attention while Narsena focuses on the Lich. Raust skillfully evades the Ogres' attacks, demonstrating an almost supernatural awareness of their movements. He uses a tactic to make one Ogre accidentally strike another, causing confusion and allowing him to reach the Lich. Though the Lich dodges Raust's thrown knife, Raust calls out to Narsena, who then swiftly defeats the Lich. With the Lich gone, Raust and Narsena easily defeat the remaining Ogres.
After their successful dungeon crawl, Raust and Narsena discuss their earnings. Narsena reveals that their haul is worth enough to buy a house, shocking Raust, who realizes he was severely underpaid by his former party, receiving only a fraction of what he was worth. This revelation deeply affects him, but he resolves to focus on the future.
At the Adventurer's Guild, they encounter the receptionist, who cruelly mocks Raust, calling him a "parasite." Narsena, fiercely loyal, defends Raust and refuses to sell their materials at the guild, leading them to find another buyer. Raust is deeply touched by Narsena's unwavering support.
Meanwhile, Margulus and Saberria, having forgotten they expelled Raust, are preparing for a rematch with the Hydra. They are joined by a new healer, Lyra, and Amelia. Margulus, still arrogant and dismissive of Raust's contributions, believes they will easily succeed without him. However, during the fight, Lyra's warnings about needing specific medicine are ignored by Margulus. The battle quickly turns against them, with Amelia being poisoned. Margulus, driven by fear, abandons his injured companions, followed by Saberria. Lyra, despite her exhaustion, stays behind to tend to Amelia and eventually escapes.
Back at the inn, Lyra is furious with Margulus and Saberria's cowardice and their mistreatment of Amelia. She learns from Amelia that Raust was the one who purified Hydra poison, a feat beyond Lyra's current capabilities, and that Margulus and Saberria lied about Raust's abilities. Lyra, now disillusioned with her new party, contemplates her options.
The narrative then shifts to Raust's perspective, where he learns from Narsena that he was severely underpaid by his former party, "Lightning Sword." He realizes they exploited him. The story also reveals that Narsena had a prior encounter with Raust where he, despite his limited abilities, bravely protected her. This experience inspired her to become stronger and join him. She is shocked by how much Raust has grown in strength and skill, realizing he is far more capable than she initially believed.
The final chapters detail the "Lightning Sword" party's disastrous second attempt to defeat the Hydra. Their arrogance and disregard for Lyra's warnings lead to their downfall. Margulus, prioritizing his own safety, abandons his injured comrades, while Saberria follows suit. Lyra, despite her exhaustion, bravely rescues Amelia. The Hydra, weakened by its previous encounter with Raust, was still a formidable foe, and the "Lightning Sword" party's incompetence and greed ultimately lead to their defeat and humiliation.
