沙展高輝完成臥底任務多年，一直走不出陰霾。高輝被調往重案組警署警長方梓翹所屬警區，二人於查案期間逐漸磨合，建立默契。梓翹工作拼搏，難以兼顧家庭，兒子更與小混混結交而陷入危機。火鍋店老闆娘盧倩雯當年少不更事，為社團頭目羅威誕下女兒盧小寶，兩母女幸得高輝關顧。成為KOL的小寶為博出位不惜犯險，揭露毒品交易情況，漸漸步入無底深淵……為了保護摯親，高輝、梓翹當上黯夜的守護者，誓要將黑勢力連根拔起！

沙展高辉（陈展鹏饰）完成卧底任务多年，一直走不出阴霾。高辉被调往重案组警署警长方梓翘（陈炜饰）所属警区，二人于查案期间逐渐磨合，建立默契。梓翘工作拼搏，难以兼顾家庭，儿子更与小混混结交而陷入危机。火锅店老板娘卢倩雯（陈敏之饰）当年少不更事，为社团头目罗威（李国麟饰）诞下女儿卢小宝（江嘉敏饰），两母女幸得高辉关顾。成为KOL的小宝为博出位不惜犯险，揭露毒品交易情况，渐渐步入无底深渊⋯⋯为了保护挚亲，高辉、梓翘当上黯夜的守护者，誓要将黑势力连根拔起！

沙展高輝完成臥底任務多年，一直走不出陰霾。高輝被調往重案組警署警長方梓翹所屬警區，二人於查案期間逐漸磨合，建立默契。梓翹工作拼搏，難以兼顧家庭，兒子更與小混混結交而陷入危機。火鍋店老闆娘盧倩雯當年少不更事，為社團頭目羅威誕下女兒盧小寶，兩母女幸得高輝關顧。成為KOL的小寶為博出位不惜犯險，揭露毒品交易情況，漸漸步入無底深淵……為了保護摯親，高輝、梓翹當上黯夜的守護者，誓要將黑勢力連根拔起！

Sergeant Ko Fai completed undercover operations many years ago, and there is always a cloud hanging over him. Ko Fai is reassigned to a police precinct that is Crime Squad Station Sergeant Fong Chi-kiu’s territory. While investigating cases, the duo gradually familiarize with each other and develop tacit understanding. Chi-kiu is so dedicated to her job that she has no time for taking care of her family. Her son hangs out with the wrong crowd and gets into trouble. Hotpot restaurant lady boss Lo Sin-man was naive when she was young as she slept with gang boss Law Wai and gave birth to a girl called Lo Siu-po. Fortunately, Ko Fai has always taken care of Sin-man and her daughter. Siu-po becomes a KOL and wants to step into the spotlight by engaging in reckless maneuvers. She gradually descends into the abyss as she reveals how drug dealers go about their business. To protect their loved ones, Ko Fai and Chi-kiu become guardians of the night and are determined to eradicate the villains!

ซีรี่ย์แนวสืบสวน/สอบสวน อาชญากรรมและจิตวิทยาเนื้อหาเข้มข้น กดดัน อึดอัด และลึกลับ ครบทุกรสชาติ แห่งปี 2022 เรื่อง Against Darkness หรือ คู่เดือดสืบคดีโหด จากนักเขียนมือทองอย่าง ซอลอีนา ดัดแปลงจากนวนิยายที่เป็นชีวิตจริงของ “ควอนอิลยง” นำมาสร้างเป็นซีรีย์โดยได้ผู้กำกับ ‘พัคโบรัม" ที่ได้นำเอานักแสดงมากฝีมือมาร่วมแสดงบทบาทตัวละครหลักอย่าง คิมนัมกิล, จินซอนกยู, คิมโซจิน, และ โอคยองจู ซีรีย์เรื่อง Against Darkness (2022) คู่เดือดสืบคดีโหด

Sau nhiều năm nằm vùng, trung sĩ Cao Huy (do Trần Triển Bằng đóng) được điều đến tổ trọng án, dưới sự dẫn dắt của cấp trên là Phương Tử Kiều (do Trần Vỹ đóng). Mặc dù đã thay đổi môi trường làm việc, nhưng Huy vẫn còn ám ảnh về quá khứ và giữ lối phá án cũ. Điều đó khiến anh và Kiều thường xuyên xích mích. Tuy nhiên, sau nhiều lần vào sinh ra tử, họ bắt đầu hợp tác ăn ý và thân thiết với nhau hơn.

Về phần Kiều, cô vốn là mẹ đơn thân, sống cùng con trai đang tuổi vị thành niên, tên Hà Tử Tuấn (do Dương Khải Bác đóng). Vì mải mê phá án, Kiều ít có thời gian ở bên con, khiến Tuấn vô tình kết bạn với người xấu và bị lợi dụng.