Mainland Chinese police officer Captain Zhang encounters a Hong Kong man named Choi who has just been in a car accident caused by chemical poisoning. Zhang immediately senses something fishy about him. It turns out Choi is indeed a drug manufacturer closely linked to the notorious drug lord, Li. To save himself, Choi agrees to help Zhang arrest Li by disguising himself as a buyer in order to lure Li into a drug deal. Right before this undercover operation is about to bear fruit, Zhang realizes all too late what truths he's not detected all along.