LauKong leads a group of elite constables who investigate strange mysteries from all across the country. His position gives him authority over local magistrates and even the six ministries. Kenneth Ma, with hiscombination of bravery and wit, is Lau Kong's favourite subordinate. However, they go their separate ways after disagreeing on a robbery case. Kenneth and his wife Selena Li disappear for nearly ten years. When the case finally comes to an end, the aging Lau Kong orders Power Chan, Pierre Ngo and Lin Xia Wei to find Kenneth and ask him to rejoin the team.
Together,the four constables solve many mysteries together, but conflicts often arise due to their different personalities. Kenneth and Selena also experience difficulties and separate because of a misunderstanding. WhenKenneth meets a prostitute (also played by Selena) who looks exactly like his wife, he feels lost and delirious. Meanwhile, the Jurchens are preparing to attack the Song Dynasty. Kenneth discovers that the Jurchens have planted a spy amongst the constables. His good friend, Raymond Cho, is unwittingly used by the Jurchens. Others subsequently fall into danger as well. It becomes difficult to distinguish between friend and enemy, leaving everyone feeling insecure...