《同谋》是一部寰宇娱乐有限公司出品的剧情片，由彭顺执导，郭富城、张家辉等人主演。这部影片是《C+侦探》和《B+侦探》的续集。

影片中，泰国私家侦探陈探（由郭富城饰演）年幼时父母失踪，长大后成为私家侦探，并在调查案件时得知父母已经死亡，决定找到杀害父母的凶手。他最终发现凶手可能就是当年父母的朋友柴叔，于是前往马来西亚寻找线索。

在此过程中，陈探接到电话得知家中被盗，于是连夜赶回家，发现房子被翻得乱七八糟，床下的暗格也被搜过一遍，什么都没剩下。陈探明白父母的死亡并不是单纯的意外，于是他找到了马来西亚的私人侦探郑风喜（由张家辉饰演），并雇佣他协助自己调查案件。

郑风喜当时正处于财务困境中，为了赚钱而答应了陈探的请求。然而，马sir（由李晨浩饰演）找到郑风喜，要求他帮忙寻找当地最大的毒枭的藏身之处，以便让他牢中的弟弟脱罪。于是，在帮助陈探寻找线索的同时，郑风喜也在调查毒枭的行踪。

两人刚开始行动就被人跟踪，最终陈探受伤逃脱，而郑风喜被人偷袭打昏，衣服上被写下了威胁性字样。与此同时，柴叔也遭到袭击，下落不明。陈探跟踪柴叔的养女芷慧（由江一燕饰演）来到波叔的地方，得知波叔也是当年知情人之一。波叔给了陈探一卷录音带，据称是当年他的父母留下的证据。但是，在他们结束谈话后，波叔就被撞死了。

Chen Tan (played by Aaron Kwok) went to Thailand as a private detective to find their whereabouts when he grew up because his parents disappeared when he was young. During the investigation, it was discovered that the parents had already passed away. He vowed to find the killer who killed his parents, and tried his best to find out that his parents' good friend, Uncle Chai, is now in Malaysia. So I went to find Uncle Chai, but I was told that Brother Peng, who knew the truth back then, was dead. At this time, Detective Chen received news that his home had been stolen, so he was even more convinced that the death of his parents was not an accident, so he found Malay private detective Zheng Fengxi (played by Zhang Jiahui). Zheng took over the task because of lack of money. Help investigate the hideout of a local drug lord. The two were followed during the investigation, Chen Tan was wounded and escaped, Zheng was knocked out, and Uncle Chai disappeared suddenly. Tan Tan followed Uncle Chai's adopted daughter Zhihui (played by Jiang Yiyan) to find Uncle Bo, who was killed shortly after Uncle Bo gave him the evidence tape. Zheng felt that Chen Tan's case was too difficult, and he did not want to participate any more, and was about to leave. A group of people who killed Uncle Bo rushed up to surround them, arousing Zheng's sense of justice, and decided to help Chen find out the truth of the year