Winter, 1379. French privateers threaten London itself, the very heart of the nation. The situation becomes dire when an English flotilla of warships, with the colossal God's Bright Light among them, drops anchor in the Thames; during the first night, the entire watch of the ship disappears without a trace. Sir John and Brother Athelstan are summoned to resolve the mysteries onboard the warship, and in this fifth outing (following The Anger of God), they find themselves in the thick of a bloody battle on the Thames.