[1][3] [4][5] On January 1, 1983, New Year's Eve celebration, high school teacher Ji-hwan (Jo Jeong-seok) proposes to his colleague and girlfriend, Yoon-Jung (Im Soo-Jung).

Shortly after his proposal, Yoon-Jung notices her purse has been slashed and emptied which prompts Ji-hwan to run after the robber.

On New Year's Eve celebration in 2015, rookie Detective Gun-woo (Lee Jin-wook) and his colleagues try to find a suspect in the crowd.

While Gun-woo was reviewing surveillance videos of a street, he noticed a woman walking by who looked similar to Ji-hwan's fiancée, Yoon-jung.

Ji-hwan then ran into the suspect who was hurriedly exiting the restroom with hands that were now bloody and was carrying a woman's purse.

So-Eun turns out to be working in the same school where the couple taught and is helping Gun-woo put the pieces of events together.

However, after growing closer to each other, So-Eun appears to be killed with the same method as Yoon-Jung and other victims from the past which revealed that the serial killer may still be alive.