Episode 8 of *Mary Kills People* opens with a poignant scene as Ye-na pays a visit to her mother's grave, standing solemnly amidst the silent stones. Just then, her phone rings, delivering urgent news about Gun-soo. Without hesitation, she rushes to the hospital. Finding him, she reassures him with a tender embrace, telling him she's at peace with whatever decision he chooses to make. Gun-soo, appearing resolute, declares he's ready to proceed, prompting Ye-na to officially instruct So-jeong to take him on as a client.
Meanwhile, at the morgue, Ji-hoon and his fellow detectives uncover the grim truth: Kim Si-hyun was fatally shot before being callously dumped into the lake. The revelation casts a long shadow over their investigation.
In another corner of the city, Gwang-chul finds himself in the company of a wealthy man named Jin Yeong-su. Jin had attempted to travel to Switzerland for euthanasia, but his deteriorating health thwarted his plans. Sensing an opportunity, Gwang-chul extends the same offer, and Jin, desperate, agrees to pay any price demanded.
Back at So-jeong's, she informs Ye-na and Gun-soo that the necessary drug is not yet in her possession, necessitating a wait. Seizing the moment, they decide to embark on a seaside getaway. Meanwhile, Dae-hyun takes Song-yi out for the day. She expresses a wish to visit the spot where her mother's shopping cart is stored. There, she retrieves a cherished blanket from the basket, a relic from the days she would curl up and sleep while her mother worked tirelessly.
However, their peaceful outing is abruptly interrupted when Gwang-chul's henchmen locate Dae-hyun. In a tense confrontation, Dae-hyun is compelled to send Song-yi home alone in a taxi. The goons then escort him to meet Gwang-chul, who reveals his plans involving Jin Yeong-su. Sensing the gravity of the situation and wanting to shield So-jeong, Dae-hyun volunteers to carry out the task himself.
Upon arriving at Yeong-su's opulent residence, they are greeted by Yeong-su's lawyer, who lays out stringent conditions: the death must be entirely painless. Any hint of suffering would render the contract null and void.
That evening, as dusk falls, So-jeong spots Ji-hoon waiting outside her house. Her initial reaction is one of irritation, threatening to sue him for harassment. But Ji-hoon, earnest in his intentions, explains that he's there to protect her, warning that whoever killed Si-hyun might pose a threat to her as well.
At the beach, Gun-soo shares a heartfelt moment with Ye-na, expressing his desire to see their father, who resides in a nearby nursing home. Initially hesitant, Ye-na eventually relents. Together, they visit the hospital, where Gun-soo, with a heavy heart, informs his father of his impending death. His final wish is for their father to apologize to Ye-na, hoping it will free her from the burden of resentment. But their father, consumed by anger, merely storms away, leaving behind a trail of unresolved emotions.
Elsewhere, Gwang-chul reaches out to An Tae-sung, insisting on the return of his belongings—the drugs currently languishing in the police evidence room. Tae-sung, without hesitation, instructs his junior to carry out the task. Meanwhile, Dae-hyun engages in a conversation with So-jeong, yet deliberately withholds the truth about his dealings with Gwang-chul. He consents to procure more Bafron for Gun-soo. Shortly after, Dae-hyun receives a call from one of Gwang-chul's associates, revealing that the date for Jin Yeong-su's demise has been fixed for the upcoming Saturday.
Following their unsuccessful attempt to visit their father, Ye-na reassures Gun-soo that she will thrive even in the absence of an apology from him. She then proposes the idea of hosting a farewell party for Gun-soo, complete with a performance by his band.
The day of the commemorative party dawns, and Gun-soo's friends gather in full force. The twins are taken aback when their father unexpectedly appears at the venue. This time, he extends a heartfelt apology to both his children, causing Gun-soo's eyes to well up with tears. As he departs, Ye-na hands him a thick wad of cash—it appears she had bribed him to come and deliver those words. So-jeong witnesses this exchange, and Ye-na clarifies that she wants Gun-soo to depart without any lingering concerns.
As the party progresses, Dae-hyun receives another call and rushes off to meet Jin Yeong-su. He administers the drug with a steady hand, and once Jin Yeong-su succumbs, Gwang-chul informs Dae-hyun that this is merely the beginning. Back at the police station, Ji-hoon and his team uncover the distressing truth that someone within the police department has pilfered the drugs from the evidence room.
At the party, the moment arrives for Gun-soo's performance. He even coaxes Ye-na onto the stage to join him. After the performance, the twins exchange their final goodbyes, and Gun-soo peacefully passes away. A flashback reveals him recording a heartfelt message for Ye-na, where he refers to her as his other half and urges her to lead a fulfilling life.
