An is working undercover in a triad organization, with his sights set on the big boss, Dai Lo. But after An reports back to his boss that he's met Pinky, Dai Lo's girl, he's informed he'll be transferred—never to do undercover again. After another undercover agent is killed, and An is summoned, he'll have to figure out how to court their trust.
阿安是臥底探員，以「馬伕」身份掩飾，向黑幫頭目老大的手下炸彈、前情婦Ｐｉｎｋｙ等人套取資料。阿安把收集的情報向上司稟告，上司告知阿安：臥底任務的期限將至，他不久會復職，調往證物房。上司又訓斥他辦事不力。另一名臥底探員失手被擒，黑社會執行家法，阿安唯有自戕，離開現場，然後報警。他接到手機短訊，獲黑幫小頭目巨龍召見。阿安與黑幫嘍囉在途中遇上警察，阿安為了博取他們的信任，竟然向警察……
