The Sandbox - All Quest Adventure Land Chapter 1 - The Secret of Red Eye Walkthrough

The player, who transferred to Adventure High School, joins a Adventure Club and meets a classmate ‘Ha-Ri Koo.’
They receive a case request: “Students are missing from the school. Please find and rescue them!”
To get a key to a classroom, the player arrives at the teachers’ room and find out that students are absent due to an infectious disease that make their eyes red. The students with ‘Red Eyes’ are taking ‘Red medicine’ from the health room.
At the health room, the player discovers the fact that the ‘Red medicine’ have a high probability of causing fatal side effects.
In an underground passway connected to the health room, the player encounters a suspicious person wearing a suspicious mask. At the moment, the player thinks it was ‘You Kyung-seo,’ but at the moment he/she goes to faint.
The player wakes up in an inpatient room at a shabby hospital, and the room is looked outside.
After finding clues throughout the room, the player gets out of the room and finds a mysterious vent passageway.
Outside the passageway is zombies swarming around! How come the hospital has so many zombies?
What made this wicked mystery, and who is the villain behind the mystery?
Explore the clues throughout the land and solve the mystery!

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Thx