The following version of this book was used to create the guide: Byeong-mo, Gu. The Old Woman with the Knife. Hanover Square Press, 2022.

Gu Byeong-mo's novel The Old Woman with the Knife is written from the third person point of view. The novel employs both the past and present tenses. Scenes set in the narrative present are written in the present tense. Scenes set in the past are written in the past tense. As the narrative progresses, flashbacks accrue, thus revealing new details from the main character Hornclaw's sorrowful former life. The following summary relies upon the present tense and a linear mode of explanation.

Sixty-five-year old Hornclaw has been an assassin for over 40 years. Although she is of retirement age, she is reluctant to give up her work with her so-called disease control agency. Indeed, Hornclaw has been a disease control specialist since she was a young woman. She and her former lover and friend, Ryu, founded the agency together. Ryu saved her life when her family cast her out. She became reliant on him and thus adopted his trade. After his wife and child were murdered, Hornclaw and Ryu became intimate. Ryu was killed not long later when he jumped in front of a bomb to save Hornclaw's life.

Without Ryu, Hornclaw's life was emptied of love, of meaning, and of hope. She therefore decided to keep the disease control business running, because it was the only thing that gave her a sense of structure and purpose.

In the narrative present, Hornclaw continues to work as an assassin. Every day, she fears that her supervisor Mr. Sohn will let her go because of her age. When she is not at work, she spends her time at home with her dog Deadweight, her only remaining companion in the world.

One night, after Hornclaw is severely injured on a job, she drives to her usual clinic to see Dr. Chang. Because Dr. Chang has a deal with the agency, he will not reveal her work to the authorities. She is therefore shocked and terrified to discover that the doctor at the clinic is not Dr. Chang, but a young internist named Dr. Kang. Although Kang saves her life, Hornclaw believes she will have to kill him to protect herself. Kang, however, promises to keep her secret if she does not report him for using the clinic's resources to help his father.

Following her meeting with Kang, Hornclaw feels a new sensation. She is unsure why she feels moved by the doctor's kindness. She ends up visiting the local market where Kang told her his parents run a fruit shop. She meets Kang's mother, father, and daughter Haeni. Witnessing the family's closeness fills Hornclaw with longing.

Because of her attachment to the Kang family, Hornclaw is worried that her colleague and nemesis Bullfight will harm them to harm her. Indeed, Bullfight has had a vendetta against Hornclaw since his childhood, when Hornclaw assassinated his father. He therefore kidnaps Haeni in order to lure Hornclaw into a trap. Desperate to keep the girl safe and to repay Dr. Kang for his kindness to her, she goes in search of Haeni. She soon meets Bullfight at an abandoned construction site. The rivals end up in a brutal battle, during which Hornclaw kills Bullfight and Haeni goes free.