Firefighter Kim Ja-Hong (Cha Tae-Hyun) dies in the line of duty and is escorted to the afterlife by 3 guardians, Haewonmak (Ju Ji-Hoon), Lee Deok-Choon (Kim Hyang-Gi) and their leader Gang-Rim (Ha Jung-Woo). He finds out that that they are to escort and defend him in 7 trials in 49 days. If he passes the trials, he will be reincarnated and his guardians will be given credit towards their own reincarnation.
In the first court, Hell of Murder, Ja-Hong is tried for the indirect murder of his colleague, his superior, in a fire where Ja-Hong allegedly left him to die. He is about to be sentenced when it is revealed that he had done so only on the orders of his superior, had saved the lives of 8 others in the incident and had attempted to go back to rescue him only to be held back by other colleagues. The judge determines that the murder charge was groundless and Ja-Hong is freed.
In the 2nd court, Hell of Indolence, where those who whiled away their life in laziness and inaction are punished. Ja-Hong was presented by his guardians as someone who spent his free time helping others and working. Ja-Hong blurts out that he only worked for the money and was about to be punished when Gang-Rim interjects that the only reason Ja-Hong did so was to earn money support his ailing mother and his brother. Ja-Hong’s actions are determined to be selfless and he is freed.
On the way to the Hell of Deceit, Ja-Hong learns that one of the perks of being reincarnated would be that he would be given the ability to communicate to anyone living through their dreams once. Along the way they are attacked by ghouls and notice the physics of Hell beginning to operate differently. This change indicates that a member of Ja-Hong’s family had died with a grudge and has become a vengeful spirit. Gang-Rim leaves the party to investigate and the rest make their way to the court. In the Hell of Deceit, Ja-Hong is accused of writing fake letters to the family of those who had died, one of whom is Ji-Yeon, the daughter of his fallen superior, making him a liar. Gang-Rim manages to use a connection he has with Deok-Choon to defend his actions, stating that Ja-Hong had also written fake letters to his mom to cheer her up, allowing her to focus on her health. His letters to Ji-Yeon, despite her actually understanding that her father was dead, also helped her to cope with her loss. The evidence is thrown out and the charges are dismissed.
Gang-Rim determines that it is Ja-Hong’s brother Soo-Hong who has become the vengeful spirit. He travels to Soo-Hong’s military camp, where the buzz is that Soo-Hong, who was about to be discharged, had deserted and was nowhere to be found. He finds that Soo-Hong has been accidentally killed while on guard duty by his partner Dong-Yeon, and his death was covered up by his superior Lieutenant Park. Gang-Rim foils an attempt by Soo-Hong to kill Dong-Yeon, and learns that the reason for Soo-Hong becoming a vengeful spirit wasn’t Ja-Hong leaving and not coming home till he was a dead body, but his anger and sense of betrayal towards Dong-Yeong and Lt Park.
Dong-Yeon tips off the Soo-Hong’s mother on the location of his body and attempts suicide. He is saved by Gang-Rim on Soo-Hong’s request after the latter agreed to cooperate.
Ja-Hong, Haewonmak and Deok-Choon, pass through the Hells of Injustice and Betrayal without trial. In the Hell of Violence, Ja-Hong is tried for beating up Soo-Hong when they were younger and the latter was suffering from malnutrition. As Ja-Hong was not forgiven, he is convicted and is about to be punished when Gang-Rim instructs Deok-Choon to request for a combined trial at the next court, the Hell of Filial Impiety, as the situation is linked. The request is granted.
Ja-Hong reveals that the motivation for him beating up Soo-Hong was that; at that time, the family were poor and their mother was ailing. Ja-Hong has intended to suffocate his sleeping mother then kill Soo-Hong and himself from a drug overdose but was discovered. In a fit, he beat up Soo-Hong and fled the family home in shame and guilt, opting not to be a burden and dedicate his life to supporting them.
Gang-Rim, Soo-Hong and his mother arrive at the army base only to witness her shabby treatment at the hands of Lt Park. Enraged, Soo-Hong transforms back into his vengeful spirit form and lashes out, damaging the army base in an attempt to harm Lt Park and only stopping when he realizes how his actions are affecting Ja-Hong in the afterlife.
At the Hell of Filial Impiety Ja-Hong is immediately judged by Yeomra to be guilty. He learns that on the night of his attempted murder-suicide, he had assumed that his mother was sleeping when he was about to suffocate her, when in reality she was awake and aware and had decided to allow it, knowing that she was a burden on her family; with his sins also compounded by him being away from his family for 15 years and not seeking forgiveness. Soo-Hong, with the help of Gang-Rim and Haewonmak, enters his mother’s dream and learns that she had already forgiven Ja-Hong for that night. Since sins that have been forgiven in the living world are not allowed to be judged in the afterlife, Ja-Hong is allowed to be reincarnated.
Gang-Rim realizes that Yeomra had been meddling with his investigation in the living world. He decides to confront Yeomra directly and chooses Soo-Hong to be the next and last soul that the guardians need to attain their own reincarnation.