Mary Kills People

A patient named Hyun-woo appears in front of doctors So-jeong and Dae-hyun, who secretly provide assisted dying to terminally ill patients, and requests assisted dying.

Because of Woo-mi, So-jeong's secret is in danger of being revealed. Meanwhile, So-jeong's feelings for Hyun-woo cross the line as a doctor.

Dae-hyun accepts Soo-young's request to assist him in his death and grants his final wish. Meanwhile, So-jeong is caught in a police trap while trying to help Hyun-woo.

So-jeong makes a dangerous deal with drug dealer Gwang-chul to obtain assisted death drugs. The police investigation into So-jeong is becoming increasingly pressing.

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

When patient Yun-hee suddenly dies at Maria Welfare Hospital, So-jeong and Father Yang are investigated by the police as suspects of murder.

Dae-hyun is offered a judicial deal. Meanwhile, Ye-na's older brother, Geon-su, visits So-jeong and asks her to help him.

Ye-na goes on a final trip with Geon-su, and Gwang-chul starts a business of assisted death targeting the rich, which brings him into conflict with So-jeong.

Dae-hyun declares that he will not assist in assisted dying, and Hyun-woo finds Dae-hyun strange and goes to see him at Maria Welfare Hospital.

So-jeong is attacked by the police at the scene of an assisted death due to Gwang-chul's scheme. Unable to stand by and watch, So-jeong steps in herself.

So-jeong decides to save Mi-young and asks Hyun-woo for help. Hyun-woo demands she confess everything...

Dae-hyun, who has just been released from prison, visits So-jeong, who works at Maria Welfare Hospital. Meanwhile, Seon-ju, a terminally ill breast cancer patient, appears before them.