A chemical weapon deal arouses terrorist group Argunbia’s interest, eventually evolving into a theater hostage incident. SDU officers Cheung Ka-hin (Bosco Wong), Ko Chi-lok (Ron Ng) and Yu Hiu-yan (Sisley Choi) are implicated while on leave. They and OCTB Inspector Ho Ka-bo (Jeannie Chan) are stranded at the scene. SDU Chief Commander Fan Siu-fung (Moses Chan) is assigned the task of dealing with the enemy at this critical time. With the assistance of SDU Support Team Leader Cheung Wai-wah (Eddie Cheung), Siu-fung leads SDU to engage the terrorists in a battle of wits and fortitude. The crisis is eventually defused with corresponding internal and external coordination. However, identity of the chemical weapon buyer still cannot be ascertained, and terrorists, who are eager to swing into action, continue to lurk around in the background. Hong Kong faces the most severe security crisis in its history. While on a mission to save hostages in a kidnapping case, SDU is deceived and suffers heavy casualties. Former SDU officer Chin Bok-man (Joe Ma) is appointed as the new Chief Commander. He selects elite officers from SDU and other police departments for organizing a special squad, namely S Team. Faced with looming disasters, S Team collaborate with Interpol officer Hui Chun-fei (Michael Miu) in vigorously preventing toxic biochemical weapons from wreaking havoc in Hong Kong.
一單化學武器交易，引來恐怖組織瓦干布的覬覦，進而演變為劇院挾持人質事件。正值休假的飛虎隊員張嘉軒(黃宗澤飾)、高子樂(吳卓羲飾)、余曉欣(蔡思貝飾)被牽連其中，與O記警探何家寶(陳瀅飾)一起被困現場。飛虎隊總指揮范少鋒(陳豪飾)臨危受命，在支援組組長張偉樺(張兆輝飾)的協助下，率飛虎隊與恐怖分子鬥智鬥勇。最終裡應外合，成功解除危機。然而，化學武器賣家身份成迷，恐怖分子仍在暗處蠢蠢欲動，香港面臨有史以來最大的安全危機。飛虎隊在營救一宗綁架案人質時誤墮陷阱，死傷慘重。前飛虎隊成員展博文(馬德鐘飾) 受命擔任新總指揮，並挑選飛虎及警隊各部門精英，組織特別小組S Team。面對重重危機，S Team 與國際刑警許俊飛(苗僑偉飾）一同聯手，極力阻止生化武器病毒在香港蔓延。