动作巨星元豹（陈奕迅 饰）走红二十余载却从未得到过最佳男主角，因与泰国黑帮老大“八面佛”交好而被怀疑参与跨国贩毒犯罪，铁杆迷弟铁柱（李荣浩 饰）通过擅长“潜规则”的副导（崔志佳 饰）潜入元豹新电影的剧组，努力配合警方收集证据想为偶像洗脱嫌疑。在经历了恋上女一号童童（李一桐 饰），得罪元豹经纪人泰格（陈国坤 饰），晋升成为男二号，目睹偶像用替身、耍大牌等一系列啼笑皆非的“娱乐圈初体验”之后，铁柱也终于离案件更近了一些……

鐵柱（李榮浩 飾）一直是港產警匪片的鐵粉，從小就立志要當個除暴安良的好公安，可惜因患有哮喘而無法投考紀律部隊，惟有成為一個私家偵探。他接了案子，來香港揭開一個整容明星的真面目，沒想到被香港警方威迫利誘參與一項臥底任務 -- 調查他的偶像、國際武打巨星元豹（陳奕迅 飾）！根據線報，元豹與綽號八面佛的泰國冰王（鄭冀峰 飾）過從甚密，警方懷疑他們透過拍戲進行不法勾當！

Tiezhu (Li) is a private eye recruited by the police to investigate the criminal activities surrounding action icon Yuen Bao (Chan). A long-time fan of Bao’s, the asthma patient Tiezhu can hardly believe his luck when he saves his idol’s life during a set accident. But as the two become friends and Tiezhu is brought in to reshape the sci-fi action film that Bao is working on, Bao’s sneaky manager, Tai (Danny Chan Kwok-kwan), is determined to turn his action crew into drug traffickers.