ong - so o ▁at ▁the ▁hospital ▁and ▁asks ▁him ▁to ▁co oper ate ▁so ▁that ▁he ▁can ▁catch ▁the ▁k iller ▁for ▁him , ▁but ▁D ong - so o ▁does ▁not ▁comp ly . ▁Instead , ▁D ong - so o ▁orders ▁his ▁men ▁to ▁find ▁the ▁k iller ▁through ▁a ▁sketch , ▁and ▁they ▁manage ▁to ▁find ▁his ▁car ▁and ▁a ▁kn ife . ▁D ong - so o ▁eventually ▁inform s ▁T ae - su k ▁of ▁the ▁find ings , ▁and ▁they ▁decide ▁to ▁team ▁up ▁to ▁catch ▁the ▁myster ious ▁k iller . ▁D ong - so o ▁agre es ▁to ▁provide ▁man power ▁and ▁cover ▁exp enses ▁— ▁but ▁on ▁the ▁condition ▁that ▁the ▁k iller ▁belongs ▁to ▁the ▁one ▁who ▁finds ▁him ▁first . ▁D ong - so o ▁wants ▁to ▁kill ▁him ▁for ▁reven ge ▁while ▁T ae - su k ▁wants ▁to ▁arrest ▁him ▁in ▁order ▁to ▁solve ▁five ▁connected ▁murder ▁cases ▁and ▁then ▁eventually ▁get ▁promoted . ▁▁ ▁Meanwhile , ▁D ong - so o ▁orders ▁his ▁right - hand ▁man , ▁K won ▁Oh - s ung , ▁to ▁kill ▁his ▁rival ▁He o ▁Sang - do ▁with ▁the ▁k iller ' s ▁kn ife ▁that ▁already ▁has ▁the ▁blood ▁im print s ▁of ▁the ▁k iller ' s ▁previous ▁vict ims . ▁An ▁en rag ed ▁T ae - su k ▁gets ▁into ▁a ▁fight ▁with ▁D ong - so o ▁upon ▁learning ▁what ▁he ▁has ▁done ▁as ▁the ▁killing