Inspector Joy

Yi Eon is a food-loving ordinary young man who works at the palace. One day, one of the secret royal inspectors comes back seriously ill, and Yi Eon is chosen as the next secret royal inspector. Meanwhile, Jo Yi who wants to get a divorce from her current husband Chu Han needs evidence that he is a gambling addict in order to make it happen. When she asks her best friend Bo Ri to help her, but she tells her a piece of shocking news.

The sudden death of a maiden, and a suspicious magistrate. Even though Yi Eon is not interested in investigating crimes, he could not turn a blind eye to this case. Therefore, he starts to search for evidence at Bo Ri's tavern. Meanwhile, Jo Yi finds the account book at Bo Ri's, and she realizes that it belongs to the magistrate of Gaehwa Valley.

Thanks to the help of Yi Eon, Jo Yi finally gets approval for her divorce. Soon after, an assassin shows up at Local Office, and Yi Eon happens to find out about those accused of criminal conspiracies. Meanwhile, Jo Yi leaves Gaehwa Valley to get to Hanyang and ends up staying the night at a shrine.

Yi Eon and Jo Yi run into a ghost. Jo Yi realizes that the ghost bears a striking resemblance to someone she knows. She starts chasing after it and soon discovers the ghost's secret. Meanwhile, Yi Eon and Jo Yi hear that Soyang Trading Group is riddled with corruption. They infiltrate the group to save the kids suffering under the tyrannical leader, Cha Mal Jong.

Yi Eon protects his people with the sword as the Crown Prince has taught him. As Jo Yi tries to convince Tae Seo and Mal Jong with her sharp observation, Yi Eon is impressed and wants to keep her with him. Meanwhile, Park Seung sends his son, Do Soo, to Tae Seo when he hears about Tae Seo getting involved with a new secret royal inspector. 

Yi Eon manages to capture one of Mal Jong's men, who were chasing Jo Yi, and gets a clue about their hideout. They plan to barge into it to find more evidence about Bo Ri's death and the account book. Meanwhile, Do Soo is also curious to know where Tae Seo gets his expenses and decides to visit his hideout himself. 

Yi Eon and Jo Yi manage to chase Tae Seo away from his hideout. As Yi Eon receives the crown prince's prescription from his bodyguards, he notices that he has been taking too much aconite before he died. Meanwhile, after running away from his hideout, Tae Seo sets traps around his mine so Yi Eon and his people cannot disturb him again while extracting the silver.

Yi Eon visits a relay station nearby to summon backup to suppress Tae Seo's silver mine. However, he gets shocked after he sees the dead body of Seok Gi on the ground and figures out someone else is going after Tae Seo as well. Meanwhile, Bi Ryeong has no choice but to help Do Soo find Tae Seo's mine, where he has set up poisonous traps.

Jo Yi, Gwang Soon, and Bi Ryeong travel to Tail Island to find Jo Yi's mother. When they get off at Ganghwa Island, they run into Han Gi and ask her about Turukson. Meanwhile, Yi Eon comes back and surprises everyone after secretly investigating Tae Seo and Do Soo's family. Naturally, Park Seung gets disappointed that he is alive. 

Jo Yi runs into Seung Yul, her childhood friend who became a successful lawyer in Hanyang. As they are catching up with each other at a tavern, Yi Eon stops by and sees them together. Meanwhile, after Tae Seo loses everything he worked for, he feels betrayed by his father. He plans to kill not only his father but the King as well. 

Jo Yi, Bi Ryeong, and Gwang Soon start to make a living in Hanyang by making clothes and reading fortunes for noble ladies. Jo Yi hears all sorts of information about Park Seung's family from their gossip and relays the messages to Yi Eon. Meanwhile, Jo Yi's mother finally visits her in Hanyang with the help of her friend. 

Yi Eon finds out Tae Seo was the fake physician who poisoned the Crown Prince to death. He wants to reveal that Park Seung was behind it but, Director Sim stops him as there is no point in arresting him when the King is on his side. Meanwhile, Jo Yi hesitates to hand over the gunpowder ledger to Yi Eon as she knows that her mother is involved. (

Yi Eon continues to go after Park Tae Seo who fled from the execution, but he fails in catching him. Yi Eon gets removed from his position and starts to blame himself. Then, Jo Yi shows up before him and cheers him up. They go out together and happen to spend a night at Yi Eon's place. The next day, Yi Eon is summoned to the palace by the royal order and appointed to a new position by his new supervisor.

Yi Eon's grandmother continues to pressure Yi Eon to marry a woman she chooses for him. Yi Eon resists until the day he leaves for Ganghwa Island in order to catch Park Tae Seo. In the market, Jo Yi runs into Seung Yul who now works as a lawyer. Seung Yul sincerely tells his feelings for her with a gift that Jo Yi wanted to have years ago. Meanwhile, Park Tae Seo finds out a secret about his birth and falls into a state of panic.

Yi Eon receives evidence from Tae Seo that Park Seung was the mastermind in poisoning the crown prince. Jo Yi witnesses Park Seung hiding a letter inside the sock that he had specially made. Tae Seo head to Hanyang to testify against his father's crimes, but Park Seung and Do Soo head to Ganghwa Island.

Yi Eon takes Park Seung to the edge of a cliff before taking him into the Department of Justice. Although given one last chance to repent for his sins, Park Seung does not show any signs of remorse. Later on, Yi Eon finally resigns from his post. He tells Yuk Chil and Gu Pal about his plans for the future which shocks them both.