In the summer of 1666, the English fleet is divided in mysterious circumstances, and Matthew Quinton, his crew and his friends are heavily outnumbered by the Dutch. The colossal Four Days Battle that ensues, the greatest sea fight in the entire age of sail, forms the basis of the narrative. In its aftermath, Matthew is tasked with investigating exactly how false intelligence came to be believed, leading to the division of the fleet. This leads him into a dangerous mission in Plymouth, a hotbed of republican sympathies, before he returns to lead his ship into the second great battle of the summer, the St James’ Day Fight.