Episode 10 of *Mary Kills People* kicks off with a series of fleeting flashbacks. Ji-hoon manages to persuade Dae-hyun to join forces with them. Dae-hyun consents, but with a couple of stipulations—he will shoulder the blame for all the euthanasia cases, sparing So-jeong, and their primary focus must shift to apprehending Gwang-chul.
Subsequently, Dae-hyun convinces Gu Gwang-chul to personally deliver the drug to the client's residence. Gwang-chul agrees, but An Tae-sung alerts him about the trap before he arrives at the apartment. Gwang-chul, in turn, informs Dae-hyun. Dae-hyun then unveils the hidden bugs to So-jeong, who promptly springs into action, orchestrating a scenario that makes her visit appear as a routine medical consultation.
The detectives, sensing Dae-hyun's exposure, burst into the apartment. Yet, So-jeong stands her ground, leaving the police with no concrete evidence to arrest her. Later, Dae-hyun and Ji-hoon explain to the other officers that their true target was Gwang-chul. Yi-soo, furious at Dae-hyun for deceiving her, declares that she will no longer serve as his lawyer. She then pays a visit to So-jeong's residence, vowing to do whatever it takes to bring her down.
Meanwhile, Dae-hyun pleads with Ji-hoon to release him, proposing to act as the decoy that would lead to Gwang-chul's capture. Ji-hoon acquiesces, fitting him with an ankle monitor. Elsewhere, Park Min-seong (the nephew of Park Tae-hyung) urges Gwang-chul to expedite his uncle's demise, despite the looming police threat. Gwang-chul agrees, demanding half of Min-seong's inheritance in return.
At the police station, Councilman Baek presents An Tae-sung with a news report about a corrupt officer. He warns Tae-sung that his name will soon be tarnished in the media and advises him to resign. However, Tae-sung pulls out a recorder containing evidence of Baek's own misdeeds, coercing the councilman into allowing him to remain in his position.
Ji-hoon attempts to secure a warrant for Gwang-chul's office, but An Tae-sung denies the request. At the welfare hospital, Father Yang inquires of Ye-na whether she collaborates with So-jeong as well. Ye-na confesses her involvement, attempting to justify their actions as a means to alleviate people's suffering. Back at So-jeong's hospital, she receives a threatening message from Gwang-chul in the form of a compromising photo he took of her. Nevertheless, she remains resolute in her refusal to cooperate with him.
At school, Jae-yeon files a formal complaint of school bullying against Woo-mi, alleging that Woo-mi has been systematically isolating her from her peers. The school administration promptly contacts Yi-soo to inform her of the situation. Later that same day, Woo-mi summons Jae-yeon to a bustling department store, where she unveils a video featuring So-jeong and Ji-hoon—a scene from earlier in the show when So-jeong nearly administered Bafron to Ji-hoon, mistakenly believing him to be a patient.
Woo-mi, with a menacing glint in her eye, threatens to make the video public unless Jae-yeon withdraws her complaint. Jae-yeon, undeterred, counters by pointing out that the video's release would also implicate Yi-soo. Just as Jae-yeon is about to depart, Woo-mi, in a fit of rage, begins smashing items in the store. Suddenly, Gwang-chul materializes out of nowhere and settles the bill for the damages.
Jae-yeon, feeling shaken, calls So-jeong to recount the harrowing incident. Concerned for the well-being of the children, So-jeong reluctantly agrees to comply with Gwang-chul's wishes. He instructs her to meet him at Park Tae-hyung's residence that very evening.
Upon her arrival at Park Tae-hyung's house, So-jeong is taken aback to discover that they expect her to play a role in Min-yeong's death as well. However, So-jeong firmly refuses, drawing a line in the sand. Min-yeong, sensing her resolve, eventually asks So-jeong to merely look after her husband in his final moments.
The husband and wife share a poignant farewell, their emotions raw and unfiltered. Tae-hyung then drinks the glass of champagne that So-jeong offers him. As Tae-hyung succumbs, Min-yeong, her heart heavy with sorrow, rushes to the edge of the roof and hurls herself into the void below.
The police soon arrive on the scene, and Ji-hoon is taken aback to find An Tae-sung already present. An Tae-sung claims to be an acquaintance of Park Min-seong. Later, when Park Min-seong heads to the morgue, he receives a staggering blow upon realizing that the deceased woman is not his aunt.
Back at the hospital, So-jeong discovers a new patient in her ward who has sustained injuries from a fall. Upon closer inspection, she is shocked to recognize the woman as Min-yeong. Meanwhile, Ji-hoon arranges a meeting with the father of Soo-young, the terminally ill teenager whom So-jeong had helped pass away a few episodes prior. It appears that Soo-young’s grandmother harbors suspicions regarding the circumstances of her death. Once Soo-young’s father becomes aware that So-jeong is in jeopardy, he steps forward and takes the blame upon himself. He recounts to Ji-hoon the immense suffering Soo-young endured and how her passing was a serene release from pain.
When Min-yeong regains consciousness, So-jeong breaks the news of her mother’s demise to her and confesses her lingering doubts about whether she did the right thing by assisting her mother. This inner turmoil, she explains, left her unable to help Min-yeong at that critical moment.
Dae-hyun contacts Gwang-chul and informs him of a new client willing to pay a higher sum than Park Min-seong for euthanasia services. Gwang-chul provides him with an address to procure the Bafron. However, upon arriving at the location, Dae-hyun finds himself ambushed by Gwang-chul’s henchmen.
Ji-hoon approaches So-jeong and shares the news of Soo-young’s father’s selfless act. She requests some time to process the information. Subsequently, she calls Gwang-chul and requests Bafron to handle the situation with Min-yeong. Meeting Gwang-chul, she proposes that they should formally collaborate as partners.
In the interim, Park Min-seong arrives at the hospital and, in a shocking act, places a pillow over Min-yeong’s face.
