In the spring of 1217, Lincoln is not a safe place to be. A French army has captured the city, and the terrified citizens huddle in the rubble of their homes as the invaders stalk the streets and attempt to smash down the walls of the castle, the last remaining loyal stronghold in the region. Edwin Weaver, the son of a rural commoner who has risen rather abruptly to become part of the personal household of Earl William de Warenne, finds himself riding straight towards Lincoln as part of a relieving army led by the legendary regent William Marshal. To add to his confusion and fear, his lord the earl has just volunteered him for a dangerous mission: he must infiltrate the city, find the resistance, identify the traitors, and return to apprise the regent of the situation. The last man who attempted such a thing was captured by the French, his head hacked off and catapulted over the castle wall as a warning.