When a terrorist who specializes in explosives takes hold of an underground tunnel, he threatens to kill hostages if his demands are not met.

JS Cheung (by Andy Lau), a Superintendent in Explosive Ordnance Disposal Bureau (EOD) of Hong Kong Police Force, went undercover seven years ago into the gang led by the most-wanted crime boss Peng Hong (by Andy Lau). Cheung successfully uprooted the gang and arrested a few robbers including Hong's younger brother Biao. However, Hong was on the loose and he swore he'd be back for revenge. Seven years have passed and Hong kick starts his plan - a series of bomb attacks have sparked fear among Hong Kong citizens. To maintain law and order, Cheung must put Hong behind bars and he is ready to sacrifice his life to fight a tough battle with the ruthless bomber.