South Korea\'s top most wanted criminal, nicknamed \"Helios\" (Chang Chen), and his assistant, nicknamed \"Messenger\" (Janice Man), have successfully stolen a mass destruction weapon secretly developed by the South Korean military, the portable nuclear explosive device DC8 along with sixteen raw material spheres. The police forces of Hong Kong, China and South Korea were informed that \"Helios\" will hold an underground trading in Hong Kong.
An emergency response team was set up in Hong Kong. Its members, chief inspector Lee Yin-ming (Nick Cheung) of the Counter Terrorism Response Unit, senior Chinese official Song An (Wang Xueqi), and two South Korean weapon experts Choi Min-ho (Ji Jin-hee) and Park Woo-cheol (Choi Siwon), work together to trace the whereabouts of the weapon. Lee also specially invites Physics professor Siu Chi-yan (Jacky Cheung) of the University of Hong Kong to serve as a special adviser for the operation.
Hong Kong, China and South Korea face the same objective, but with different purposes. Choi wants to hunt down \"Helios\" to take back the weapon to make sure not to divulge secrets of South Korea. In the position of the Chinese government, Song wants to resolve the current crisis in Hong Kong and halt any terrorism activities in Chinese territories. Lee and Siu face pressure from the two countries and have to deal with the greatest challenge since the establishment of Counter Terrorism Response Unit, with the situation getting more tense.
As times passes by each second, with \"Messenger\" arrested and DC8 falls into the hands of the Hong Kong Police Force, China and Korea fight for the right to possess the weapon. On the other hand, \"Helios\" appears in Macau, with plans to retaliate and repossess the weapon. During the last stand, conspiracies are gradually revealed, with everyone off guard.
A city with no awareness of any crisis meet with world\'s largest crisis.