Diarmait Mac Murchada was a king through misadventure. Owing to a series of fatal family mishaps he was elected to power in 1126 at sixteen. He ruled through a turbulent period and became one of the most dominant figures in Irish history.

Furlong presents a thorough account of Diarmait's life and examines his actions and decisions not only in the context of his questionable personal traits and character but also expanding the analysis to reflect on his effect on the political turbulence of the time. At one stage of his influential life, ousted as King of Leinster, he invited King Henry II of England to assist him in regaining the throne. The subsequent invasion marked the beginning of eight centuries of English dominance. After his death he was damned as a traitor and a blackguard. He is recorded as having two wives at the same time, raping an abbess, the abduction of Dervorgilla, the wife of his bitter rival, and the mutilation and killing of rivals.

Furlong's Diarmait King of Leinster is a subtle, compassionate yet realistic examination of the man behind the myth.