Ryung officially becomes a member of the Wangsoori Subway Police and Ji Seok’s partner. Ryung gets into trouble from the start, because she sneaks into the tunnels. Meanwhile, an elderly man who delivers packages via subway becomes the victim of an assault. Ji Seok realizes that the package is related to criminal activities. While Ji Seok wants to hand the case over, Ryung acts before she thinks, as always. (Source: Viu)