This is the last entry to the pocketbook.
They quickly escape from the room with the remaining cast and also quickly leave the Lab and head for the Control Room as the zombies are chasing them.
Dong-hyun searched the bathroom and a chained zombie Byungsil appeared.
As doom, his only role was watching over humans for eternity and not be able to have any emotions or whatsoever.
Next to the TV monitor is a key to the Basement.