This is the third in the Rosemary Sutcliff Series about King Arthur and the knights of the round table but it doesn't matter what order you read them in. I haven't read any of the other Rosemary Sutcliff books in this series but I still really enjoyed this book because I already knew a lot about Arthur and because the story is more or less stand alone.
The Quest for the Holy Grail is over and their are only a few of Arthur's best knights left. These are the days when darkness begins creeping in and Arthurs long forgotten sin is finally remembered. Arthurs destruction always makes me cry, he is such a kind warm hearted man and yet he suffers the worst things anyone could imagine. His wife, son and best friends are divided against him and things that seemed long forgotten are brought to light. The worst betrayal is that of Lancelot, he is my favourite of Arthurs knights but although he tries to withstand it he is Arthurs ultimate downfall- the weakness, the only way to penetrate the round table from outside and bring about the end of Camelot.
If you enjoy stories about King Arthur another really good book to read is The Once and Future King by T. H. White which begins when Arthur is a young boy and ends at the destruction of the round table. There are many different books about King Arthur all with slightly different variations but my favourites are the ones by Rosemary Sutcliff and the ones by T. H. White.
I won't say any more, you must read them for yourself and find out. All I will say is that I really enjoy stories about King Arthur and his knights and Rosemary Sutcliff writes about them particularly well.