Ultra serious Ko Lap and carefree Kung Kwan are expert assassins.It's love at first sight for Kwan when he runs into the lovely Bin Yee. And Ko Lap continues to hide his love for Sau Yu, agent for him and Kwan. Unkowingly, Ko Lap executes a contract on Yee's father.

CID officers Ho Tin-nam (Michael Chow) and Jacky Wong (Hilary Tsui) follow a stray dog to the crucified body of a truck driver in a remote area. Much of the suspicion centres on his fellow trucker Chan (Shing Fui-on), particularly when the victim's wife is killed as well. When not only Chan, but the nosy stray dog are added to the growing number of victims, attention is focused on an arrangement which the drivers had with a Chinese prostitute named Yin-fong. She had been their secret liaison in Shenzhen, and committed suicide when the men refused to let her stop providing her services to them. Yin-fong's twin sister Mei-ping (Miki Ng) also becomes a suspect, but yet another murder provides her with an alibi. Officers Ho Tin-nam and Jacky are faced with a plethora of red herring leads and an escalating body count before they can bring the real killer to justice.

The sequel to Thou Shalt Not Swear. Chow reteams with Lau to investigate a murder and his wife is a suspect this time. All the murder victims seem to have cheated on their wives.