三名北爱尔兰首府贝尔法斯特的菜鸟警察要为正义而奋斗，却发现他们要对抗的是贩毒集团、准军事组织、卧底特务、当地社区，甚至是自己人。一场大规模的当地犯罪帮派调查行动戛然而止后，重重困难与危险问题随之浮现。是谁在保护这些罪犯？又为何要保护他们呢？

　　Grace, Annie and Tommy are growing up fast as police officers, but nothing can prepare them for the turmoil they face every day. It’s a year since the fall of the McIntyre crime gang and the vacuum has been filled by rival gangs, all competing for dominance. Constable Shane Bradley is drafted in to help, but his motivations are unclear. Tommy is dangerously seduced by the world of intelligence policing, while Grace struggles to deal with her son’s absence, and growing feelings for fellow officer Stevie. As a young loyalist threatens to take over the city, the officers face a major gangland feud – culminating in a violent and devastating confrontation.

　　一个受保护的证人在转移途中遭伏击，三名在场警察被杀害，负责这次转移的探长Lindsay Denton很快被怀疑串通罪犯，反贪组在调查Denton的同时，也在寻找真凶，但是事情似乎并不简单……

　　BBC宣布一次性续订《警之光》两季。