Mary Kills People

A terminal patient, Hyun-woo, requests assisted death from the doctor, Wu So-jung (Lee Bo-young), and her assistant Dae-hyun (Kang Ko-young).

Wu So-jung begins to cross a line as she develops feelings towards Hyeon-woo (Lee Min-ki)

So-jung and Dae-hyeon become trapped, as the police investigation closes in.

So-jung makes a dangerous deal with a drug dealer Gwang-chul (Baek Hyun-jin) in order to acquire the euthanasia drug. The police investigation into the case is becoming increasingly fraught.

So-jeong, who brought Si-hyeon out of the hospital, is found injured and abandoned on the street. Dae-hyeon, who finds out about this, goes to find Gwang-cheol.

When patient Yoon-hee (Yang Jo-ah) suddenly dies at Maria Welfare Hospital, So-jeong (Lee Bo-young) and Father Yang (Kwon Hae-hyo) are investigated by the police as suspects for murder.

Dae-hyun (Kang Ki-young) is offered a judicial deal. Meanwhile, Ye-na's (Yoon Ga-i) older brother, Geon-su (Kang Ki-dong), visits So-jeong (Lee Bo-young) and asks her to help him.

Yena (Yoon Ga-i) goes on a final trip with Geon-su (Kang Ki-dong), and Gwang-cheol (Baek Hyun-jin) starts a business of assisted death targeting the rich, which brings him into conflict with So-jeong (Lee Bo-young).

Yena (Yoon Ga-i) embarks on her final journey with Geon-su (Kang Ki-dong), and Gwang-cheol (Baek Hyun-jin) clashes with So-jeong (Lee Bo-young) as he begins a business of assisted death targeting the rich.

So-jeong (Lee Bo-young) is attacked by the police at the scene of an assisted death due to Gwang-cheol's (Baek Hyun-jin) scheme. Unable to stand by and watch, So-jeong (Lee Bo-young) steps in herself.

So-jeong (Lee Bo-young) decides to save Mi-young (Woo Mi-hwa) and asks Ji-hoon (Lee Min-ki) for help. Ji-hoon (Lee Min-ki) demands she confess everything...

Dae-hyun (Kang Ki-young), who has just been released from prison, visits So-jeong (Lee Bo-young), who works at Maria Welfare Hospital. Meanwhile, Seon-ju (Kim Young-ok), a terminally ill breast cancer patient, appears before them.