If All the Swords in England is a beautiful book about St. Thomas Becket. I called this post a "sort of a review" because I'm actually going to cheat and send you to Alicia's terrific review at Love2Learn. It can be found here, and summarizes the book and characters wonderfully. And, I see that Alicia and I even left out the same line when reading this book aloud (Ramona was in the room, so I skipped a couple of other details as well.)
This book (dubbed "Sif all the Words in England" by Ramona, thanks to the cover design) held Anne-with-an-e and Betsy captive all the way through, their interest never waning. They were nearly as moved as I was when St. Thomas was killed (though I think I'm the only one who actually wept.) Seeing the action from the young twins' point of view was particularly moving, and left an imprint on my girls that a straight narration of the facts would not have accomplished.
Quick detours had us looking up more information about King Henry II, discussing the responsibilities of the Church vs. the state, and looking (very) briefly into Eliot's Murder in the Cathedral.
I love, love, love this way of studying history with my children. It comes alive and stays with them in amazing ways.
If you're looking for some historical literature but don't know where to start, try visiting the Reading Your Way Through History page for ideas. It's never steered us wrong!