Heretic from the Grail Quest series is a easy book to read full of adventure and tension. It is set in the 14th century and is about Thomas a English archer and his adventures around a mission to find the Grail. It is based in history and the beliefs of the time but is mainly fiction. I have read the first and last books in this series and enjoyed them, not sure why I have ended up reading them out of order though. However it is easy to get into the swing of the story even if you have missed a bit.
Well worth reading the series especially if you have an interest in the times of the 100 years war.