The title says it all. This book might be found in your library, but if not just go ahead and buy it. It's a near-perfect blend of modern style with period feel. So it reads like a modern novel, but the characters have nearly no anachronistic problems, nor does the plot. It got such favorable commentary I bought mine straight away and have no regrets, having read it a few times at this point! My re-issue was from nyrb classics around 2010:
In 10th C. Denmark, Orm is being held a bit tightly by his mother on the homestead. The plot races along quickly when a ship pulls in at night to steal some food, including some of his family sheep. Orm ends up having two big adventures, one West and the other East. He meets famous people, and many interesting not-so-famous people. It has everything a gamer could want and presents the wonderful complexity of the time without degrading any of the characters or religions present - not even Christianity - !!!
Plus, his characters have a real sense of humor that is also NOT anachronistic, but we still enjoy it today.
Lots more here at Amazon, where it has 223 reviews and nearly 5 stars, an amazing feat: