In 1651, a fatally wounded Scottish trooper is found by an English patrol. Before he takes his last breath, he reveals the details of a major plot being hatched against Scottish leaders and English generals within Clarke Castlethe same castle where many kidnapped Scots are being held.

Luke Tremayne and his sergeant, Andrew Ford, have just arrived in Oban, Scotland, via the English republics newest man-of-war, the fifty-four gun Providence. As the warship remains anchored in the sea loch, Luke and Andrew come ashore to receive details of their mission from their new ally, David Burns, a man of considerable wealth and passion for his cause. After Burns briefs Luke on the Scots three political groups, six assailants press up the stairs to Burns chambers and deliver a pouch that contains a coded message. Luke soon discovers that he must not only rescue the prisoners at Clarke Castle, but also must uncover the local leadership of this organization created by the King.

As Scottish leaders plot and murder their way to a solution, Luke becomes embroiled in a conspiracy to murder the political elite and quickly finds out that an ally is not who he appears to be.