Episode 6 of "Hyper Knife" kicks off with a nostalgic flashback, where Deok-hee engages in a thoughtful conversation with Dr. Song. Dr. Song reveals how he lured the young and academically brilliant Se-ok from another institution, recalling her arrival at the welcome ceremony accompanied by her social worker. He confides in Deok-hee about Se-ok's unpredictable demeanor and her entanglements with loan sharks for financial gain, subsequently unveiling her residency application form. In the present moment, Deok-hee still clutches that yellow slip of paper, a tangible reminder of the past.
His thoughts are interrupted by a call from Min, who presents him with an intriguing proposition. The scene transitions to Min's boat, where Deok-hee, Se-ok, and the rest of the team are instructed to surrender their phones. Se-ok's anger still simmers, and Min clarifies that the mysterious client has specified Deok-hee as the lead surgeon for this operation.
On the boat, Hyeon-ho and Young-joo begin preparing for the surgery, with Young-joo expressing his concerns about Se-ok potentially losing her composure towards Deok-hee. Meanwhile, Se-ok is on the deck, casting her dogs' collars into the sea in a fit of rage. Deok-hee approaches her, revealing a startling truth: he had euthanized her dogs to shield her from police scrutiny. His cold confession only fuels her fury, prompting her to attack him with her umbrella until Young-joo intervenes.
Se-ok storms off to her room, slamming the door behind her. Min warns Young-joo in a stern tone to keep her under control; otherwise, none of them will make it off the ship alive. When Young-joo inquiries about the client's identity, Min responds cryptically, "It's God."
Elsewhere on the boat, Hyeon-ho suggests to Deok-hee that he should consider undergoing surgery by his friend, Kwok Song-tae, a renowned doctor at another hospital. Deok-hee, however, insists that Se-ok is the best option, emphasizing that he himself has molded her into the surgeon she is today. Hyeon-ho gently reminds Deok-hee that his students do not owe him anything, a sentiment that echoes deeply.
Elsewhere, Mrs. Ra picks up Alan Kim from the airport and chauffeurs him to Deok-hee's residence, setting the stage for a possible new chapter in the narrative.
In the early morning light, Deok-hee encounters his patient, an enigmatic figure revealed to be a revered godman battle-scarred by cancer. Bound by his religious beliefs and an army of devoted followers, he finds himself unable to seek treatment in conventional hospitals. Elsewhere aboard the vessel, Min discreetly informs Se-ok and the team that the surgical procedure will unfold under the cloak of night, as per the patient's request. Hyeon-ho unveils the patient's true identity: Kim Eun-tae, a notorious cult leader whose influence spans far and wide. Se-ok, concerned, confides in Hyeon-ho about Deok-hee's less-than-optimal hand condition, urging him to keep a vigilant watch during the delicate operation.
Back at the police precinct, Inspector Yang faces a pressing deadline of one week to track down Min. Shortly thereafter, two officers confront Min's subordinate, Pyo In-guk, who surrenders Min's contact information to Yang. The inspector promptly initiates a grilling interrogation, probing for insights into Min's whereabouts.
As dusk descends, Deok-hee administers a medication to himself. Kim Eun-tae,escorted to the operating theater, is taken aback by Se-ok's youthful demeanor and demands an elaboration on the surgical procedure. Sensing Deok-hee's potential unease, Se-ok offers to swap roles should his hands betray even the slightest tremor.
The surgery commences, with tensions rising. At a crucial juncture, Deok-hee inadvertently grazes a blood vessel, sparking a small hemorrhage. As they navigate through the surgery, Deok-hee's words turn pointed, accusing Se-ok of ingratitude. Yet, he concedes a heartfelt gratitude towards her, acknowledging how she ignited his passion for teaching. These words strike a chord in Se-ok. Meanwhile, Inspector Yang leverages In-guk's phone to dial Min's number, narrowing the net.
Post-surgery, Se-ok discovers Deok-hee atop the deck, where he reveals that contrary to her perceptions, he harbors no malice towards her. Reluctantly, she concedes that their shared moments in the operating room hold some of her fondest recollections. She extends her heartfelt thanks, bowing in gratitude for all he has taught her.
Ha U-yeong arrives unannounced at Deok-hee's residence, assuming illness had kept him away from work. However, the butler dispels this notion, revealing that Deok-hee is out of town. Instead, U-yeong encounters Alan, who explains he is there to assist in a surgery alongside Se-ok. As Alan presents the MRI scan, U-yeong's eyes widen in recognition; it unmistakably belongs to Deok-hee. Han Hyeon-ho decides to stay behind and attend to the patient, while the rest depart from the vessel.
Mrs. Ra collects Deok-hee, and during their journey, she warns him that Min might exploit Se-ok as a pawn to coerce Deok-hee into performing additional surgeries. Intrigued, Deok-hee halts the car and delves into an old letter from Se-ok to Dr. Song. In her heartfelt missive, Se-ok confesses her awareness of Dr. Song's disapproval but her unwavering determination to become a neurosurgery resident. She elucidates her struggle with an overactive mind that consumed her appetite and sleep, only to find solace during her first brain surgery observation, where her thoughts finally stilled.
As Se-ok's narrative unfolds, parallel scenes from Deok-hee's journey from student to doctor emerge, mirroring her own experiences—from incapacitating headaches and relentless thoughts to the tranquility found within the operating room. Present-day Se-ok smiles softly upon completing the letter.
Meanwhile, Min, Se-ok, and Young-joo venture out for dinner, with Min exuding an air of suspicion. A flashback illuminates a clandestine deal Min struck with Yang, promising Se-ok in exchange for police immunity. In the present, Se-ok excuses herself to Young-joo, asking for painkillers as her headache intensifies, clearly planning to confront Min, who, in turn, intends to betray her to the authorities.
Se-ok maneuvers to draw Min aside for a private conversation. Just then, U-yeong's call interrupts, urgently informing her that Deok-hee's condition is far more grave than apparent, urging her to rush him to the hospital. As if on cue, Se-ok catches sight of Deok-hee dragging Min into a shadowy alley. Tiny flecks of blood mar the pavement behind them, signaling a dramatic climax as Hyper Knife Episode 6 draws to a thrilling close.
