A lo largo del río Mekong se encuentra el llamado triángulo dorado, uno de los mayores proveedores de droga del mundo. El gobierno chino encarga a Ko que investigue la aparición de trece cadáveres y de un cargamento de droga en el río. Por su parte, Fong, un agente de inteligencia, anda tras la pista de un temible señor de la droga. Ambos deberán colaborar, pero uno de ellos esconde un secreto.
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.
