In the summer of 1643, while bloody war rages across England, scholarly Thomas Hill receives an unexpected summons from the King, and travels reluctantly from his home in Romsey to the royal court at Oxford, leaving his widowed sister and her daughters to fend for themselves. Having learnt that his predecessor was murdered, he takes over as the King"s cryptographer. There is evidence of a traitor at court, and when a message is intercepted, encrypted with the "unbreakable" Vigenere square, Thomas thinks it will reveal his identity. His suspicions are confirmed when his old tutor and lover are viciously murdered, he is run down in the street, his room is ransacked, and he is thrown, on a false charge, into the notorious Oxford Castle gaol, where he contracts gaol fever. To reveal the identity of the traitor, and save himself, Thomas must break the "unbreakable" cipher. That will not, however, be an easy task. The King"s Codebreaker is the first in a trilogy of Thomas Hill stories. The second, Blessed Rain, is completed, and the third, Quicksilver, is underway.