A Chinese secret agent named Da-hee is receiving information that a large arms shipment is trying to smuggle into Korea, so she is assigned to investigate and try to dismantle the arms trafficking network. In the meantime, she knows Su-han, who must help her put the details of this investigation together, only because she is not made for this job at all, as she does not have enough experience and skills in this regard. , the two spend more time arguing over minor matters than investigating. But when their witness is killed, the two immediately become prime suspects.