Lee Joonbecame a vampire.
They found a file called 'Helper' in a computer at the office and they copied it onto a USB. Yoon San then found another hidden room full of blood bags.
It turned out thatLee Se-yeong's (Han Gyeo-wool) brother was a vampire and he had become one after he was bitten by his girlfriend. Han Gyeo-wool's brother swore to 'make a special blood for' her.
Yoon San wondered what 'Helper' was and Yong Goo-hyeong suggested they gave up the case.
However, Yoon San didn't give up and asked Han Gyeo-wool if there was a place where her boyfriend went to often and she said, "He goes to his girlfriend's house in the countryside".
The three of them left to find the vampire but they were being followed. They searched an old country house and was attacked by Han Gyeo-wool's brother there. He said, "I don't mind being a monster for love".
Their followers shot Yoon San instead of Han Gyeo-wool and her brother injected blood into him. Yoon San became a vampire.
Source from :Hancinema