This book (also available in French The Last Kingdom) is the first that deals Uhtred Bebbanburg of a 9th century Saxon, who fights with King Alfred the Great 'against the Vikings (or the Danes, as the calls). It is rather arrogant, and his loyalty is divided between the pious king and the Vikings who raised him from the age of ten.
There already are five books that follow the adventures of Uhtred, and a sixth will be published this year. I recommend to all who love adventure, medieval history and the bloody battles!