The story begins in the land of Daeho where mages can harness the power nourished by the supernatural lake. Among the all-respected mages is Jang Kang who is also the father of Jung Uk, the leader of the mages and an enthusiast whose curiosity brings him to the alchemy of souls.
The alchemy of souls is a powerful yet prohibited spell that can help the one performing to switch bodies, the spell that fetches the doom to Jang Kang’s personal and professional life after he exchanges his body with the fatally ill king who asks this of him.
The king take advantage of this opportunity and goes on to create an heir of his own with Jang Kang’s wife, who was completely unaware of that truth at that moment.
Jung Kang finds out that the child has been born under the King’s Star, so Jang Kang blocks the newborn Jang Uk’s energy gates to keep him safe, before disappearing.
Years later, the head of Songrim, Park Jin is seen following the infamous assassin Naksu who declares to be the one behind the deaths of many mages. Park tries to kill her and give Naksu a fatal wound but is unable to stop her from escaping.
Naksu knows her body can collapse at any time, so she rushes to perform the alchemy of souls to save herself, however, she accidentally ends up in the body of a blind, powerless girl- Mu-deok. Now, Naksu is left with no powers of her own and just a set of skills that she is unable to use, she tries to get back her sword, assuming that she will be able to get her powers back.
Later, Naksu, who is now Mu-deok meets Jang Uk who recognizes her identity because of the would shifter mark in her eyes. He makes her his private server and asks her to be his master, only to be rejected. Instead, she tries to get to her sword only to find herself trapped inside Songrim after the news of a soul shifter infiltrating the place is brought out.
Park Jin calls for the help of the Jin family as Jin Cho-yeon brings the Sapsali to find the soul shifter among them all. Fortunately for Mu-deok, a soul shifter does get caught and diverts everyone’s attention while the Sapsali chases Mu-deok. Jang Uk saves Mu-deok again but breaks Sapsali’s pottery which gets him punished.
Later, Mu-deok gives him her goodbyes and tries to go back to her place only to see her body being burned in front of everyone.
Right then, Jang Uk arrives with her sword which gives her hope. However, she’s still unable to unsheathe her sword.
Left with no hope, she attempts to end her life in the lake when the lake fills her up with power which makes it possible for her to unsheathe her sword. Realizing that immense power is needed to help her regain her energy, she accepts Jang Uk as her student.
After a poisonous battle and severe punishment, she can help Jang Uk unlock his energy gates only to find out that he is unable to control the power. The crown prince then arrives and gets into a duel with Jang Uk after he tries to take Jang Kang’s sword.
However, due to Mu-deok’s intervention, the crown prince loses. This becomes a bigger issue after Jin Mu finds this to be an opportunity to block Jang Uk’s succession to his father’s position as the Gwangju. Mu-deok and Jang Uk then escape the capital as the former takes him to the place that was her home for years.
The two reach Danhyanggok where they meet master Lee who is a pupil of the legendary mage Seo Gyeong. The two begin their days there but u-deok soon realizes that Jang Uk is not as enthusiastic about learning and tries to get him back on board. The two soon begin training and Mu-deok passes on her special skill Tansu to Jang Uk.
Elsewhere, Seo Yul reveals having met Naksu when he was younger which helps Park Jin and Heo Yeom realize that she was the missing daughter of a constellation mage who went wild after becoming a soul shifter. Jang Uk and Mu-deok return to the capital where the latter finds herself entering Jinyowon after a series of events to escape Kil-joo, only to get trapped inside the Mirror of Longing.
The relic that trapped her creates an image of herself in front of Seo Yul and the crown prince which shocks them as they rush to the Jin family house. Jang Uk too arrives there while searching for Mu-deok and the three enter Jinyowon.
Jang Uk soon finds out that Mu-deok has been trapped inside the mirror and covers it so that he doesn’t get trapped inside himself. Right then Mu-deok touches the mirror surface which cracks it, following which the two can leave Jinyowon.
Later, Kil-joo blackmails Mu-deok into bringing Jang Uk to him so that he can soul shift into his body. Mu-deok is unable to do so and reveals this to Jang Uk who tells her to go meet Kil-joo. Upon meeting, Jang Uk fights Kil-joo and can fight him but suddenly, the latter starts the alchemy and they enter the world of soul shifting.
Luckily, Jang Uk is saved by the real Mu-deok who does not let Kil-joo succeed, following which the truth behind the death of Naksu’s father is revealed. He also reveals that Jin Mu is not the real Danju as the real one has the ice stone which can help soul shifters from going wild.
He then tries to escape and reach the real Danju who is none other than the queen herself but perishes in front of the palace in Jang Uk’s hands. Jang Uk promises to bring the ice stone to Mu-deok and later wins the duel against the crown prince.
He is then scouted to join various organizations wherein he decides to join Songrim. The celebrations begin after which Jang Uk is taken back to Songrim while Mu-deok is sent back home as personal servants are not allowed to follow inside.
Left with no choice, she decides to participate in the competition to be hired in Songrim while she assures Jang Uk that she will soon follow him by passing the leaflet of the competition. The two are separated for the time being as Park Jin’s task keeps Jang Uk busy while Mu-deok participates in the contest.
Mu-deok gets help from the crown prince, Seo Yul, and Park Dong-gu and is soon able to pass all the tests in the hiring process. After the competition, Jang Uk and Mu-deok meet and he reveals her feelings that have started to bud for him. He tells her he missed her too.
Elsewhere, Jin Mu and the queen have something big planned as they work on making So Yi the fake Jin Bu-yeon with the help of Jin Woo-tak. On the other hand, master Lee and Park Jin discuss Jang Uk’s matters and the former reveals that master Seo Gyeong himself was born under the King’s Star like Jang Uk.
Park Jin later goes to a funeral where a soul shifter is found who is stabbed by Seo Yul. He later tries to catch him but Yeom Soo kills the soul shifter. But this event leaves a mark on Seo Yul who has found out the truth about Mu-deok.
The days of the duels arrive and Jang Uk loses them one after another. After his ninth loss, he follows Mu-deok into Cheonbugwan for a task when he comes across a eunuch who is a soul shifter. Jin Mu finds the two and tells the eunuch to take Mu-deok’s energy and then shift it into Jang Uk’s body. However, when he attacks Mu-deok, his energy gets absorbed by Mu-deok which shocks and scares her.
Later, Jang Uk uses his wit to call for the crown prince and the two can escape only to be left shocked when the eunuch they thought was dead is brought forward. The two can leave Cheonbugwan, but Mu-deok fears getting close to Jang Uk while the latter is brought for some fishing by master Lee who helps him reach Chisu.
The last match arrives and he finds out that Mu-deok has bet herself. He prepares himself once again, only to find Seo Yul standing against him and losses in the end. Later, Mu-deok searches for the jade that was thrown away by the crown prince and goes to meet Jang Uk. But seeing him with Heo Yoon-ok makes her jealous which instigates Jang Uk to kiss her.
Later, he is taken to the palace by master Lee along with Seo Yul and Park Dang-gu, where master Lee reveals his identity as a soul shifter. He tells the king that he has a way to find soul shifters and instigates fear in the queen and Jin Mu.
Park Jin suspects Mu-deok of the murders happening but Jin Cho-yeon helps her out while he tests Mu-deok and Jang Uk only to find out that the two love each other. The next day, Jin Ho-kyung finds a chance to create a ruckus in Songrim due to which the relationship between Park Dang-gu and Jin Cho-yeon is revealed.
The two rebel against their family and find shelter at Jang Uk’s house. Jang Uk finds out that Seo Yul is aware of Mu-deok’s truth while the queen plans to escape amidst the arising suspicions around her. Jang Uk soon goes out to find information about shaman Choi when he comes face to face with Jang Kang.
Jin Mu brings So Yi disguised as Jin Bu-yeon in front of Jin Ho-kyung. They take her to the doors of Jinyowon which opens due to the presence of Mu-deok who is standing behind the group.
Jang Uk fails to recognize Jang Kang while Ho-kyung soon grows suspicious of So Yi who is taken to an assembly and introduced as the new leader; unaware that the shaman Choi in the queen’s body is preparing to take over her body.
Jin Ho-kyung brings the ice stone in front of everyone which grows the greed of the people present while Park Jin tries to convince the mages present to destroy the stone. Jang Uk arrives and tries to delay the assembly while letting the crown prince know about his suspicions about the queen.
Later, the king wants to test the ice stone and makes Mu-deok the object of the experiment. Standing in front of Jin Ho-kyung, Mu-deok is ready to die and be brought to life. However, while being choked, memories of Jin Bu-yeon’s childhood flash by and she calls out “Mother” which shocks Jin Ho-kyung. A storm starts brewing.
Mu-deok finds herself inside the storm where she meets the real Jin Bu-yeon who warns her of the burden that she will have to carry if she uses the stone, she also gets to know that the barrier is the ice stone. She is ready to shift her soul and says her goodbyes to everyone but fails when she finds out that the barrier has been infiltrated by a soul shifter.
Aware that the mages will not be able to use their powers inside the barrier while soul shifters are strengthened, she puts a pause on her plans. However, after an attack on Seo Yul which makes So Yi put her blood worm into his body, she soon finds out that Jang Uk has put himself in danger and rushes to save him. Now aware of her strong feeling for Jang Uk, she is unable to say her goodbyes to him and gets another promise along with a kiss.
Jang Uk then finds a way to break the barrier and finds himself standing among the stars in place of the King’s Star with the ice stone in front of him. Everyone witnesses the star arising but assumes the crown prince to be behind it, except Park Jin.
The calamity soon comes to an end after the shaman Choi’s death and Jin Woo-tak’s confession. As words of parting are said to Seo Yul while celebrations are welcomed with the upcoming wedding of Park Dang-gu and Jin Cho-yeon. Jang Uk and Mu-deok too share a dream of having a wedding themself and very soon.
But good days don’t last long as Jin Mu acquires shaman Choi’s bells and puts Mu-deok under a spell to control her. On the day of the wedding, he orders Mu-deok to kill Jin Woo-tak and go wild in Songrim.
Mu-deok arrives at Sejukwon and is seen attacking Jin Woo-tak by Jin Cho-yeon and Park Dang-gu who try to stop her only to fail. Successfully killing Jin Woo-tak, she goes wild in Songrim and stabs Jang Uk which gives her a moment’s consciousness.
Jin Mu arrives at Songrim and reveals Mu-deok’s truth while tagging Jang Uk as a criminal, Jin Mu again rings the bells, and Mu-deok is completely in his control. On Jin mu’s order, Mu-deck creates a massacre on Cho yeon’s wedding day.
Following this incident, Jin Cho-yeon vows revenge while Jin Mu successfully labels Jang Uk a criminal which leaves him with a funeral fit for a criminal. However, when the fire on Jang Uk’s body is lit, a change of events turns the fire blue and shocks everyone.
On the other hand, Mu-deck is aware of what has happened and jumps into the lake which is a grave for soul shifters, only to be saved by unidentified people. On the other hand, Jang Uk is now reborn.
You can watch this series on Netflix.