<Korean TV Series NOW> ”Undercover High School” EP3, Seo Kang Joon tracks down the truth behind another ghost story = Viewership rating 6.6%, Synopsis/Spoiler

※This article contains spoilers. In EP3 of the MBC TV series "Undercover High School" (viewership rating: 6.6%), Hye-sung (Seo Kang-Joon) spreads all over the school.
The film depicts the pursuit of the truth behind another ghost story that has been told. It is revealed that the skeleton found in the ballet practice room in the basement of the old building is a model. The key found with the skeleton model also contains
Along with the official seal of the first chairman Byung-mun (Kim Eui-seong), the words "The Beginning of the Gold Nugget" are engraved on it, further strengthening the connection between the gold nugget and ghost stories.
The circumstances of security guard Kim (Koo Min-hyuk) who was at the scene were also revealed. Kim was patrolling the old building.
When he was walking down the hall, he found what appeared to be a skeleton, and when someone came down to the basement, he threw a hammer and ran away. After Hye-sung left, Kim took out the mysterious notebook from the desk drawer, but
In it was written the keyword of Byeongmoon High School's ghost story. Hye-sung visited the school in the middle of the night and while looking around, she found a keyhole on the back of the clock. In the basement of the old building
Just as she was about to insert the key she found, Myung-ju (Kim Shin-Rock), the chairman of the board, appeared and Hye-sung escaped the situation by saying that she had dropped the coin. After Hye-sung left the place, Myung-ju also
He found a hole large enough for the old-fashioned key and looked meaningfully at Hye-sung.