The year is AD 1174.

Returning to England from the Saracen Wars, Sir Michael Culhaven makes his way from the port of Tyne toward his Manor north of Alnwick Castle. Tired of war and its accompanying death, he finds no relief as he rides toward billowing smoke coming from a burning farmhouse and saves a woman and her little daughter from being attacked by Flemish mercenaries. Through an odd sequence of events a scrap of paper is eventually found inside the child's ragdoll and will soon bring Sir Culhaven face-to-face with traitors at the castle who attack him and the manor to prevent the code from being deciphered.

As William I closes in on the castle, Sir Culhaven has little time left to unravel the code and prevent the fall of Alnwick Castle.