友为人憨直,虽服务警队十年,有劳但无功。结婚七年,其妻在商界春风得意,与友生活习惯及思想行为距离愈来愈远,其妻卒不辞而别。友在查案中得知消息,大失常态,险些累及女警吴君如身陷险境,二人自此积怨……Two mismatched Hong Kong police detectives, Yau and Yue, were assigned to work undercover as a live-in couple to track down a serial killer accused of murdering adulterers. In the meantime, Yau (Anthony Chan) is coping with his girlfriend having left him, and Yue (Sandra Ng) is losing her boyfriend to a college girlfriend of his.