The Hotel del Luna (formally referred to as the "Guest House of the Moon"), located in Myeong-Dong, Seoul, is not like any other hotel: its clients are all ghosts, and it is not visible in its true form during the day. Humans can only come across the hotel under special circumstances, for example, during a Lunar eclipse.
During the Goguryeo era, a rebel named Jang Man-wol (IU) went through a series of tumultuous events that led to her committing several sins. She escaped from her captors and began her search for the "Guest House of the Moon" as she felt that she had wronged those who died because of her and held a strong grudge. She drank a liquor made with "Moon flowers" offered to her by a deity (Mago) that unknowingly turned her into the guest house's owner while she was traveling to find it. She has been stuck to the "Moon Tree" ever since and has been running the hotel for more than a 1,000 years before meeting Koo Chan-Sung (Yeo Jin-goo), the new manager. Koo Chan-Sung was deemed to be just the right person for the job by Mago as Mago believes that he holds the key to the freedom of Jang Man-Wol from the guest house.
The 16 episodes of the series depict how Koo Chan-Sung adjusts to his new ability to see ghosts, his new job, and the tantrums of his fickle new employer. The hotel has several staff members, the oldest being the bartender Kim Seon-Bi, the head wait-staff Choi So-Hee, and the doorman Ji Hyeon-Jung. Over time Koo Chan-Sung wins the hearts of all the members working in the hotel and together they serve their guests by trying their best to give them a satisfactory experience before they leave for the afterlife.
The "Moon Tree" that had seemed to be dead for a thousand years sprouts leaves and blossoms as the bond between Koo Chan-Sung and Jang Man-Wol deepens and they begin to date. The leaves and flowers begin to shed once Jang Man-Wol realises the problems and risks her hotel's manager has to face because of her and she begins to fear for his life.
Jang Man-Wol comes across several people she was acquainted with in the past which brings up bitter memories. But with the help of Koo Chan-Sung and her hotel staff, she overcomes them and moves on. Jang Man-Wol leaves the hotel to drop-off a person from her past to the bridge to the afterlife.
The days roll by and soon enough the branches of the "Moon Tree" are bare. Jang Man-Wol returns to the hotel after a month much to Koo Chan-Sung's happiness. The hotel staff and the guests leave one by one as they have each gotten their closure and because the time for Jang Man-Wol to leave the hotel forever has arrived.
Jang Man-Wol and Koo Chan-Sung share an emotional farewell as Man-Wol leaves for the afterlife alone after they both promise to meet each other in the next life. After she leaves, the hotel closes down as well.
Time goes by and Koo Chan-Sung tries to move on. He goes abroad while hoping for the best. Meanwhile, Mago has found a new owner for the "Guest House of the Moon", a man who names the place "Hotel Blue Moon". The series ends with a sense of mystery.
The new general manager of Hotel del Luna, succeeding the previous manager, Noh Joon-suk. He is a handsome HarvardMBA graduate, who is hired as an assistant manager at one of Korea's top hotel. However, he later becomes the general manager for the Hotel del Luna due to a deal his father made with Jang Man-Wol twenty years ago.
The longest employee of the hotel and the Sky Bar's bartender. He lived during the Joseon dynasty as the scholar Kim Shi-Ik, who committed suicide after being removed from his position for writing stories about the lives of commoners. He waited for 500 years to clear his name.
The housekeeper and room service provider with an extrovert personality. She also lived during the Joseon era as a nobleman's wife. When she gave birth to a girl instead of a boy, the family took her child away to starve the baby whereas her husband slept with another woman to have a baby boy, in order to carry on the family name. She was driven to insanity after her daughter's death and was killed later on by her husband's men. She vowed to see the family tree die out and wishes to take the last heir of the family with her to the afterlife.
The hotel receptionist. He is nice and polite but does not like his job. He was accidentally killed by his friend during the height of the Korean War and cares very deeply for his younger sister. He starts dating Jung Soo-Jung.
Kang Mi-na as spirit of Jung Soo-Jung/Kim Yoo-Na (residing inside Kim Yoo-Na's body)
A rich and arrogant student, whose physical body becomes the residence of the spirit of Jung Soo-Jung, a schoolmate that Yoo-na bullied and murdered by pushing her off a bridge. Yoo-Na's spirit is obliterated by her parents, and so Soo-Jung decides to remain inside Yoo-na's body and assume her identity to be able to live. She is hired as an intern.
A soldier during the Goguryeo era who fell in love with Man-Wol. He was forced to marry Princess Song-Hwa and to capture the rebels to rid the king of suspicions and to spare Man-Wol from punishment. Just after his marriage to Song-Hwa, he intentionally allowed himself be killed by Man-Wol out of his unwavering love and guilt towards her.
Man-Wol's fellow rebel who is like a brother to Man-Wol. He was captured and killed under the lead of Goo Chung-Myung, which led to Jang Man-Wol developing a deep grudge against the latter. He is reincarnated as police officer Park Young-soo, who becomes Lee Mi-Ra's boyfriend (reincarnation of Princess Song-Hwa).
Chan-Sung's friend when they were studying at Harvard. He is a millionaire and owns a pizza shop. He lives with Chan-sung in Seoul. He eventually learns the truth about the Hotel Del Luna after his girlfriend's death.
A princess during the Goguryeo era who was attracted to Chung-Myung and later marries him. She was slain by Man-Wol on her wedding night. She is reincarnated as Chan-sung's squandering ex-girlfriend Lee Mi-Ra, who later becomes Park Young-soo's girlfriend.
A rich guy who was Chan-sung and Sanchez's schoolmate in Harvard. He had defamed Sanchez but was thwarted by Chan-sung, which resulted in him being Sanchez and Chan-sung's nemesis. He later commits suicide after being outed for committing a heinous crime and becomes a vengeful spirit who aims to haunt Chan-sung and his acquaintances for revenge.