『龍根小(xiao)說』介紹:出身香港社(she)會(hui)最底(di)(di)層的丁小(xiao)嘉(佘詩曼(man)飾)在(zai)考上警察(cha)后,又(you)以臥(wo)底(di)(di)的身份(fen)重回魚(yu)龍混雜的砵(bo)蘭街(jie),替CID督(du)(du)查康道(dao)行(xing)(xing)(歐(ou)瑞偉(wei)飾)搜集(ji)(ji)情(qing)報。誰知在(zai)追查三(san)合會(hui)頭目游達富的犯(fan)(fan)罪事(shi)實過(guo)程中(zhong)(zhong),道(dao)行(xing)(xing)意外遇害身亡。他(ta)在(zai)臨死前為(wei)防止手(shou)下臥(wo)底(di)(di)人員身份(fen)暴(bao)露,而刪除了(le)包(bao)括小(xiao)嘉在(zai)內等(deng)五名臥(wo)底(di)(di)的紀錄。在(zai)此之后,道(dao)行(xing)(xing)的同(tong)袍(pao)刑事(shi)情(qing)報科總(zong)督(du)(du)察(cha)卓凱(kai)(苗僑偉(wei)飾)聯系到小(xiao)嘉,希望其(qi)能協(xie)助找(zhao)到其(qi)他(ta)四(si)名臥(wo)底(di)(di),并掌握外圍賭博(bo)集(ji)(ji)團(tuan)(tuan)的犯(fan)(fan)罪證據(ju)。在(zai)此之后,小(xiao)嘉和賭博(bo)集(ji)(ji)團(tuan)(tuan)的得(de)力(li)干將(jiang)薛(xue)家強(林峯飾)發生交集(ji)(ji),更由(you)此陷(xian)入警方與(yu)犯(fan)(fan)罪團(tuan)(tuan)伙、黑(hei)幫(bang)組(zu)織之間的連番對決(jue)和火并之中(zhong)(zhong),由(you)此上演了(le)一段令(ling)人拍案叫絕的臥(wo)底(di)(di)傳奇(qi)……