Episode 2 of "Hyper Knife" kicks off with an intense scene where Se-ok, in a fit of raging emotion, shatters Deok-hee's vial of medication, her laughter echoing maniacally through the air. Young-joo, catching the tumult from afar, swiftly dials for paramedics as Deok-hee collapses to the ground. Meanwhile, a shadowy figure with an ankle monitor keeps a distant vigil over Se-ok's residence.
A nostalgic flashback then transports us to Se-ok's residency days. She effortlessly tackles a neurology quiz stuck on the bulletin board, her eyes lighting up with excitement upon noticing an announcement welcoming back Dr. Choi Deok-hee to the hospital. We witness Deok-hee in conversation with another physician, Dr. Song, who cautions him about Jeong Se-ok, branding her as unpredictable.
Se-ok storms into Deok-hee's office, presenting him with that week's neurology quiz. She reveals that she has been eagerly anticipating his return since before her graduation and has even committed portions of his research papers to memory. Deok-hee, impressed, returns her quiz paper with the word "Perfect" scrawled across it. Later, in a scene bathed in rain, Se-ok passionately pleads with Deok-hee to take her on as his protégé.
In the present, Deok-hee confides in Mrs. Ra, reminiscing about Se-ok's fervent love for brain surgery, her desire to expire in the operating room. He admits to sharing a similar fervor at her age but regrets not recognizing her lack of self-control.
Later, Deok-hee meets with Dr. Han Hyeon-ho, Se-ok's colleague, and discusses his ailment. Han conveys the opportunity to Se-ok, urging her to undertake the surgery, highlighting Deok-hee's offer to aid in reinstating her medical license. However, Se-ok remains defiant, asserting that even with her license restored, she would still be barred from operating in hospitals. That night, driven by frustration, she burns all her residency papers, many adorned with Deok-hee's "Perfect."
The following day, the mysterious man with the ankle monitor appears at Se-ok's pharmacy. He reveals that he had been observing her the previous night and extends an invitation for a drink. After his departure, Se-ok and her pharmacy coworker witness the man brutally assaulting his older sister, the proprietor of the local diner, painting a grim picture of his dual nature.
Both of them enter the diner as patrons, driven by the determination to halt his actions. While indulging in their meals, Hyeon-ho dials Se-ok, inquiring whether she could undertake a surgery on a fresh patient that very night. Without hesitation, she consents. She attempts to reach out to Young-joo, but to no avail; he is engrossed in contemplating a photograph featuring Se-ok, Deok-hee, and another woman, which he discovered among the ashes of the papers Se-ok burned the preceding evening.
Their paths eventually cross when Young-joo encounters the woman from the snapshot. She reveals that the picture was captured on the pivotal day when Se-ok spearheaded her first surgery. She describes Se-ok as both a genius and a naive fool.
A vivid flashback unfolds, showing Se-ok's fiery reaction upon discovering that Deok-hee had overlooked her for a prestigious research program in Boston, opting instead for another resident named Ha U-yeong. Without regard for the presence of U-yeong's mother in Deok-hee's office, Se-ok bursts in and creates a scene. Enraged by her behavior, Deok-hee strikes her and subsequently bars her from participating in any surgeries. A year passes before a department head grants Se-ok the opportunity to operate while Deok-hee is absent. Upon his return, Deok-hee has her physically removed from the operating room.
In the present, Se-ok's anticipated patient fails to appear. As she and Hyeon-ho prepare to depart, she notices Deok-hee seated in a nearby vehicle and realizes his involvement in the no-show. He informs her that he has secured her a position at Boston University, where she can perform as many surgeries as she desires. However, he demands that she operate on him in return. Se-ok declines once more, yet Deok-hee remains confident that he will make it happen. Mrs. Ra, who is driving Deok-hee, cautions him to proceed with caution.
Young-joo and Se-ok venture into the neighborhood diner, where their gaze falls upon a man encumbered by an ankle monitor, his piercing eyes fixed on Se-ok. Elsewhere, Deok-hee engages in a conversation with Alan, a resident of the United States, informing him that his supply of medication is dwindling to the last vial. Alan assures him he will make the journey as soon as possible.
That very night, Se-ok catches sight of the ankle-monitored individual keeping vigil outside her residence. Venturing out, she realizes this surveillance has been a recurring theme. As she steps outside, two locals approach, initiating a chat that reveals the diner's impending sale due to the relentless financial demands the man has placed on his sister. Enraged at the prospect of losing her beloved haunt, Se-ok contemplates murder, only to be restrained by Young-joo's reasoning.
Later, Se-ok finds herself back at the diner, now acute to the absence of the ankle monitor on the man's person. Engaging in conversation, she reluctantly agrees to share a drink with him the following day. The next morning, Se-ok covertly crushes pills and blends them into his beverage.
Driving by, she spots him cycling and offers him a ride. Accepting her drink, he unwittingly consumes the laced concoction, and they soon arrive at her abode. Moments later, he succumbs to unconsciousness, only to awaken bound and center stage in Se-ok's plastic-lined living room. With a reassuring smile, she assures him all is well before slashing his throat with relentless precision.
As Se-ok transports the lifeless body into the woods, she dials Young-joo, instructing him to return home and sanitize the scene. Rushing back, Young-joo incinerates all remnants of Kwon Sin-gyu's existence, as evidenced by his ID card found amidst the ashes. Scrubbing the bloodstains from the floor, Young-joo's luck takes a turn for the worse when a policeman spots the blaze in the front yard and heads towards the house.
In the dense woods, Se-ok senses an approaching presence, springing into action, ready to defend herself. To her relief and astonishment, she discovers it is Deok-hee, wrapping up an intense episode of "Hyper Knife."
