The West Country, July 1643.

England's civil war has reached a bloody stalemate, with neither side able to secure a decisive advantage. But with a Royalist victory at Roundway Down comes an opportunity to seize the precious port city of Bristol. King Charles's flamboyant nephew, Prince Rupert, leads his army out of Oxford to snatch the prize, supported by his brother, Prince Maurice, attacking from the south. In Bristol, the Parliamentary garrison commander, Colonel Nathaniel Fiennes has to contend with a lack of manpower in a city of divided loyalties as he prepares its defences for the onslaught to come.

The ensuing struggle will harness the enmity between the two Reeve brothers: carefree and dissolute Ralph, now a corporal of dragoons in Prince Maurice's Regiment, and Francis, the embittered and fanatical puritan in the Parliamentary horse.

It will also determine the fate of Moussa Dansocko, the west African slave accused of sorcery and witchcraft and threatened with a lynching, Kedall Tremain, the fisherman turned tinner who fights for Cornwall and its king and Abel Cowans, the disabled and impoverished naval gunner from Newcastle who finds himself working in Bristol docks when the assault on the city begins, and others, all with their diverse reasons for finding common cause with one side or the other in the brutal struggles of the divided kingdom.