A Thousand Days' Promise

Ji Hyung, a betrothed man, is having a decade-long affair with Seo Yeon, a writer with a haunted past.

Seo Yeon struggles to leave Ji Hyung behind while also struggling with increasing bouts of forgetfulness.

Seo Yeon's visit to the hospital leads to a devastating diagnosis. Meanwhile, Ji Hyung feels increasingly distanced from his fiance.

Seo Yeon asks Moon Kwon to quit his part-time job. Meanwhile, Moon Kwon and Jae Min begins to suspect something's wrong with Seo Yeon's mind.

Ji Hyung confronts Seo Yeon about her disease, resulting in an emotional stand off as Seo Yeon fiercely struggles to guard her pride.

In light of Seo Yeon's creeping alzheimer's, Ji Hyung breaks off his engagement. Seo Yeon struggles to cling onto her memory.

Ji Hyung's parents are outraged with the prospect of his broken engagement. Seo Yeon tries to convince Ji Hyun to stay with his fiance.

Ji Hyung and Hyang Gi's families deal with the aftermath of their canceled wedding. Seo Yeon begins to feel increasingly lost as her disease strengthens.

Ji Hyung asks Seo Yeon to marry him. Ji Hyung's mother begins to suspect that Seo Yeon is pregnant.

Ji Hyung's mother considers supporting her son's affair. Seo Yeon's aunt seeks out her niece's mother.

Seo Yeon gets lost while driving home. Ji Hyung asks Seo Yeon to let him into her life.

Ji Hyung and Seo Yeon break news of their engagement to their loved ones. Inspired by her reunion with Ji Hyung, Seo Yeon vows to ward off Alzheimers with renewed determination.

Seo Yeon moves in with Ji Hyun. Hyang Gi discovers that her ex-fiance's new woman is an Alzheimers patient.

Ji Hyung and Seo Yeon head off for their honeymoon, but the trip is ruined when Seo Yeon begins to have bouts of nausea and pain.

Hyang Gi leaves for America. Suh Yeon's aunt begins to have suspicions about her niece's health.

Suh Yeon finally reveals the truth about her disease to her extended family. Ji Hyung's mother invites her son and daughter-in-law to dinner.

Seo Yeon decides to meet with her biological mother. Ji Hyung's father reluctantly invites his estranged son and daughter-in-law over to dinner.

Seo Yeon meets her in-laws. As she nears her due date, her condition continues to deteriorate. Her loved ones observe helplessly.

As her condition worsens, Seo Yeon refuses to hold her daughter, since she can't trust herself.

Ji Hyung has to find an alternative solution for raising their daughter. Seo Yeon reverts back into a child.