DNA Lover's third episode seamlessly resumes from the cliffhanger, where So-jin and Yeon-u plummet from the rooftop, their lives hanging by a thread. Amidst this harrowing ordeal, So-jin finds herself inexorably drawn to the alluring scent emanating from Yeon-u. Miraculously, they land on an inflatable cushion, where Gang-hun rushes to So-jin's aid, promptly attending to Yeon-u as well. It's then they realize a surprising connection - they know each other.
After reassuring Gang-hun of their well-being, Yeon-u hurries to Yoo-young's side, while So-jin seeks solace in a drink, wandering to her beloved park. As she sips, memories of her father flood her mind. Gang-hun, tailing her discreetly, engages in a heartfelt conversation about the trauma of her father's passing. So-jin bears the weight of guilt, acknowledging she saw the signs of depression in her dad yet failed to intervene. Revealingly, she and So-ri are siblings, their family fragmented long before their father's demise, their bond severed post his loss.
Gang-hun, too, grapples with self-recrimination, haunted by his inability to save So-jin's dad despite being on the scene as a paramedic. He offers comfort, escorting her safely home.
Meanwhile, Yeon-u battles lingering back pain, perplexed by his instinct to use So-jin's words to soothe Yoo-young.
The following day, Yeon-u's physician friend, consumed by thoughts of Sung-mi, joins the gym in hopes of a chance encounter. He finds her intriguing yet hesitates to initiate contact, captivated by her captivating scent.
Similarly, So-jin finds herself consumed by thoughts of Yeon-u's aroma, determined to uncover the source of her fascination. She devises a plan, first probing Gang-hun about Yeon-u's frequency at the restaurant. When that fails, she ingeniously convinces Gang-hun to accept Yeon-u's invitation for a friendly basketball game at the hospital, a strategic move to get closer to unraveling the mystery of her unexplained attraction.
She tags along, cheering fervently for the team while her heart races with anticipation, yearning for a fleeting moment to capture Yeon-u's sweat. The guys, convinced of her good luck charm status, beam with gratitude for her presence at the game. Post-match, amidst the commotion, she slyly snatches Yeon-u's jersey, only to be caught in the act by his piercing gaze. Miraculously, he chooses to overlook her actions, his curiosity lingering but unspoken. She utilizes the sweat-stained fabric to extract his distinctive aroma, realizing with a jolt of realization that she's genuinely smitten by his scent. While she finds it enchanting, A-ri scoffs, comparing Yeon-u's essence to the pungent odor of a sewer.
Emboldened by this self-discovery, So-jin musters the courage to seek Yeon-u's permission to investigate the alleged cheating gene. Parallelly, Yeon-u attends an exhibition hand in hand with Mi-eun, where they encounter Myeong Hui, an artist intimately tied to Mi-eun, addressing her as a daughter. Little do they know, Mi-eun's not the only offspring; So-jin and So-ri share the same maternal bond. One of Myeong Hui's poignant artworks unveils her tumultuous journey through motherhood, painting a picture of exhaustion and the perceived burden of her children.
At the hospital, Yeon-u's new case is met with distractions courtesy of So-jin's antics. His curiosity piqued, he hesitates to delve into the matter, fearing the answer. Fate intervenes when his friends invite Gang-hun and So-jin over for dinner. Over a meal, the conversation veers towards octopuses and their polyamorous nature, prompting So-jin to divulge her disdain for the creatures. Yeon-u, protective of his culinary preference, finds her sentiments unjust and a lively debate ensues. Amidst the heated exchange, So-jin chokes on a morsel of octopus, and Yeon-u swiftly comes to her rescue.
As the evening winds down, Yeon-u trails after So-jin, finally broaching the subject of her jersey theft. She confesses, her voice tinged with embarrassment, that she sought to unravel the mystery behind her inexplicable attraction to his scent. Yeon-u, flattered by her honesty, teases her gently, leaving her flustered and seeking refuge when Gang-hun's timely intervention offers her an escape route.
For several days thereafter, So-jin's mind was consumed with the dilemma of securing Yeon-u's permission for the infidelity gene test. After much soul-searching, she devised a plan to broach the subject during her visit to deliver the Super Teol antidote. However, Yeon-u staunchly refused, insisting that genuine understanding between a man and a woman transcended such scientific methods. He curiously inquired about her scent, eliciting a blush from her as he drew closer.
Meanwhile, Sung-mi and Gang-hun stumbled upon a blazing apartment, their instincts driving them to lend a helping hand. To their surprise, it was Mi-eun's abode. Gang-hun's heroic rescue endeared him to Mi-eun, who chastised herself for neglecting to properly connect her emergency broadcast system.
Elsewhere, So-jin, So-ri, and Myeong Hui gathered at Gang-hun's father's restaurant to honor their late father's memory. Myeong-hui, unyielding in her belief, criticized So-jin's father's weakness in taking his own life, accusing him of succumbing to depression after job loss and the inability to support his family. The trio's heated exchange escalated into a blame game, their voices echoing throughout the restaurant, drawing the attention of Yeon-u, who had also come for dinner. Overwhelmed by her mother's accusations, So-jin stormed out in a fit of rage.
Gang-hun, preoccupied with other matters, couldn't immediately pursue So-jin. Yeon-u, however, couldn't ignore her distress and followed suit. Despite his initial attempts to maintain distance, he eventually joined her at her beloved park, patiently listening as she poured out her heart. So-jin lamented the bittersweet nature of love, particularly when unrequited, and expressed her yearning to find her DNA-matched soulmate to be by his side. Touched by her vulnerability, Yeon-u found himself increasingly drawn to her and granted her wish for the DNA test.
Overjoyed, So-jin hastened to the laboratory, her heart racing with anticipation. The results, however, revealed a shocking truth—Yeon-u possessed the highest level of the cheating gene she had ever encountered. The epilogue revealed a humorous twist: in her haste, So-jin had inadvertently swapped Gang-hun's jersey for the sample, setting the stage for an unexpected revelation.
