Undercover High School

As Soo-ah recovers in the hospital following the attack during the break-in, Hae-sung and the team uncover the culprit: Lee Jun-ho, the mathematics teacher. When Hae-sung detects his father's notebook missing, he realizes that Seo Myung-joo orchestrated the break-in. After Lee Jun-ho's arrest and confession, the revelation of the school's grade-rigging scandal throws the institution into chaos. Amid the turmoil, Hae-sung stumbles upon a crucial clue to the final scary story.

To everyone's shock, Seo Myung-joo returns to the school. Unimpressed by Hae-sung, she expels him and demonstrates her power by dismantling his team. However, refusing to back down, Hae-sung and the team, including Soo-ah and her mother, devise a daring plan to infiltrate the school once more to retrieve the hidden gold bars.

The gold bars vanish just as they are within reach, and Seo Myung-joo suspects Hae-sung has them. In the vault, Hae-sung makes a heartbreaking discovery of his father's remains. Overcome with grief, he finally finds closure, but a shocking truth emerges. He learns Director Kim Hyung-bae was behind it all. Determined to uncover the whole story, Hae-sung heads to confront him alone.

Despite getting badly injured, Hae-sung manages to call Soo-ah and his team. They conclude that the only evidence they can secure is the flash drive that contains the voice recording of Principal Park murdering Director Kim Hyung-bae. After finding out that an arrest warrant had been issued for her, Seo Myung-joo decides to take a special measure to end everything.