In 1812 two mighty armies manoeuvred across the Spanish plains. They were finely balanced, under skilful leaders. Each struggled to gain an advantage. Wellington knew that if he defeated the French, he could turn the tide of the war. Good intelligence was paramount, but the French were using a code of unrivalled complexity - the 'Great Paris Cipher'. It was an unprecedented challenge, and Wellington looked to one man to break the code: Major George Scovell. Using a network of Spanish guerrillas, Scovell amassed a stack of coded French messages, and set to work decrypting them.

As a man of low birth, Scovell - even with his genius for languages, and bravery on a dozen battlefields - struggled for advancement amongst Wellington's inner circle of wealthier, better connected officers. Mark Urban draws on a wealth of original sources, including many cyphers and code-tables, to restore Scovell to his rightful place in history as the man who was the brains behind the intelligence battle against Napoleon's army and a forerunner of the great code-breakers of the 20th Century.