Recommend reading The Irish Suspect first.
In the first of this series, The Irish Suspect, Dan Delaney is a first class detective in Dublin, Ireland who was blamed for a poorly prosecuted case of a child murder, and suffered severe recriminations by the public and in his career. After three years of work, he unravels a double homicide in the case of The Irish Suspect, and public opinion sways to his favor. He is promoted to Police Commissioner and his partner, Joe Murphy, is promoted to the position of Deputy Commissioner.

In the case of The Dirty Dubliner, the previous Commissioner who had covered up the investigation of a child murder has been relieved of his duties and his reputation of brutal, personally motivated murders as well as contracted assassinations are exposed.