In 2017, Son Oh-gong (Lee Seung-gi) and Woo Ma-wang (Cha Seung-won) are in conflict with each other as they look for a true light in a dark world where evil thrives.

Having made a contract with Seon-mi 25 years ago, entitling her to seek help from Son Oh-gong whenever she calls him in exchange for letting him free, the two meet again in a fateful encounter.

One day when she walks home from school, a ghost follows her, and this is witnessed by a mysterious man in a suit and black top hat (Woo Ma-wang).

Oh-gong makes her a deal: if she puts out the five candles on the table and frees him, he promises to protect her from all dangers in her life every time she calls his name.

But after she agrees and releases him, Oh-gong steals the memory of his name out of her head and makes a run for it, leaving young Seon-mi stranded in the middle of nowhere.

Still armed with her little magic umbrella, she owns a real estate company that specializes in buying haunted houses, exorcising the spirits, and then flipping them for large profits.

Oh-gong enlists the help of Jeo Pal-gye (Lee Hong-gi), a pig demon and pop artist under Ma-wang's entertainment company, to get inside the painting.

Seon-mi, who has been a loner all her life, can't help but be touched by Oh-gong's thoughtful actions, and struggles to guard her heart against any romantic feelings because Sam-jang's tragic destiny is always to be a sacrifice for humanity against growing evil.

[20][21] Choo Ja-hyun was originally cast in the cameo role of Na Chal-nyeo, but had to be replaced by Kim Ji-soo due to pregnancy.

[25][26] According to data released by Nielsen Korea, A Korean Odyssey ranked the most-watched show of its time slot including both cable and public broadcasting channels for its premiere episode.

[27] Moreover, the series broke the record for the highest ratings for the first episode of a tvN drama in the Nielsen Korea 20-49 year-old target audience bracket.

tvN issued an apology stating that there was "a delay in the computer graphics process" and that "the finalized version of episode 2 is set to air on December 25 at 6:10 p.m.